Macronutrients
Carbohydrates
Carbs, carbohydrates, starches, and sugars. Whatever you call them, this group of nutrients has gotten some bad press lately! What exactly is a carbohydrate, what foods contain carbs (because, remember, we eat foods, not just nutrients), how much do we need to eat, and are they really bad? And if they’re really bad, how could we need them? First, carbohydrates in foods exist in two basic forms—simple and complex—and that's where the confusion begins.
Simple carbohydrates are the ones you think of as sugar. The most prevalent simple carbohydrate in foods is sucrose (white or table or granulated sugar, brown sugar, as well as the sugar that gives honey, corn syrup, and fruit their sweetness). Sucrose actually consists of two even simpler sugars--glucose and fructose--chemically combined; simple sugars made from two even simpler sugars are called disaccharides (“di” means two) and the even simpler sugars are called monosaccharides (“mono” means one). When you eat or drink sucrose, whether in the form of fruit, sweet vegetables, sweetened drinks, candy, sweet pastries, ketchup, or any of the million other processed foods that have sugar added to them, your body immediately starts breaking it down to glucose and fructose. Fructose is also present on its own in small amounts in fruit (hence the name, fructose): You may have heard or read all kinds of confusing, even frightening warnings about sugar, sucrose, and especially fructose.
Regardless of what you may have heard and read, glucose is an important nutrient: Your body, especially your brain, NEEDS glucose to function! Sucrose (sugar) is broken down to glucose and fructose in your digestive tract and at least some of those molecules travel to the liver, but for the glucose to be used where it’s needed, your pancreas must send the hormone insulin out into your bloodstream. If your doctor has mentioned your “blood sugar,” this is what is being measured—the glucose traveling in your blood--so if you have diabetes and your pancreas doesn't make enough insulin or your organs don't respond correctly to insulin, the glucose doesn't get to where it needs to go and hangs around in your bloodstream or gets passed through your kidneys to your urine, with bad consequences for your whole body...If as is the case for most of us, we consume more glucose (in the form of sucrose) than our bodies need, the excess is converted by the liver and fat cells to fat. What if we consumed too little glucose? Our bodies can make it but at a cost: Starving people and those who adopt very low-calorie diets or diets completely lacking in carbohydrates actually must rob their muscles. In response to a hormonal signal, muscle proteins are broken down to their component amino acids (see “Proteins”), which are then converted to glucose as needed. Persons who adopt a very low-calorie diet to lose weight quickly are advised to eat large amounts of protein to offset this pillaging of muscle but it is unavoidable.
What about the fructose part of sucrose or the fructose in fruit? Despite what you might read and hear, even by some supposedly reputable nutritionists, we don’t fully understand what happens to fructose in our bodies. We know that, along with some glucose, fructose travels to the liver, where it can be converted to glucose. Fructose, for reasons we don’t understand, is also readily converted to fat (more easily than glucose is converted to fat). This would not be a health concern if we consumed sucrose and fructose (glucose+fructose) only in the form of fruits, vegetables, legumes, and whole grains, where the amounts of fructose are small. But many of us consume massive amounts of sucrose in the form of sugar-sweetened drinks, candy, cookies, cakes, pies, pastries, breakfast cereal, and flavorings (including, yes, honey and maple syrup). The supposedly high levels of fructose in high-fructose corn syrup are exaggerated but the existence of this sweetener is a major nutrition concern nonetheless: Made from corn, it is extremely inexpensive to manufacture compared with the sucrose from sugar beets and sugar cane it has replaced. As a result, it has been widely adopted by food manufacturers, resulting in much cheaper soda and sugar-sweetened processed food products, resulting in vastly increased sugar consumption. Our bodies may not have evolved to handle those amounts of sugar, including fructose, except to convert them into fat, resulting in liver damage (the liver begins to store this fat), damage to other organs, and weight gain.
Milk also contains a simple disaccharide sugar called lactose, a combination of the monosaccharides glucose and a sugar called galactose; many people lose the ability to digest lactose to glucose and galactose after the first year of life, resulting in "lactose intolerance." However, the microorganisms that reside in our digestive tracts are only too happy to feed on the lactose, resulting in… “gas!”
Complex carbohydrates in foods include starches and fiber. Starches are found in abundance in grains and grain products (for example flour, bread, pasta, snack foods, cookies and cakes, cereal, rice, and beer), legumes (like lentils, garbanzos, peas, kidney beans, and peanuts), and in “starchy” fruits and vegetables (think potatoes, winter squash, corn, carrots, and bananas). Fiber is found in fruits, vegetables, whole grains like whole wheat and brown rice (think “bran”), and legumes. Starches and fibers are long, chain-like molecules, where the hundreds of rings of the chain are the monosaccharide, glucose; thus, starches and fibers are also called polysaccharides (“poly” means many). So how do starches and fibers differ? Starches are actually molecules of glucose linked in a form that our digestive systems can break down: Starches are broken down quite efficiently in the digestive tract, producing molecules of glucose, which then do all the things the glucose from simple sugars does.! The glucose rings of fibers, on the other hand, are linked in such a way that our digestive systems can't break them apart; as a result, fiber itself contributes no calories to food. BUT the microorganisms that naturally reside in our lower intestines do digest fiber and appear to use it as their nutrients,, and we are only just beginning to understand and appreciate that these microorganisms—bacteria and some fungi—seem to play various roles in keeping us healthy. We also are beginning to understand that when we consume starches and sugars in the form of high-fiber foods like whole wheat bread and fruit, the fiber those foods contain helps to slow the body’s absorption of glucose, resulting in less pressure on the pancreas to produce a rush of insulin. Therefore, high fiber foods are a healthier way to consume carbohydrates than highly processed foods. Still, the so-called starchy vegetables (again, potatoes, corn, winter squash, and carrots) and the grains contain much more starch than fiber, so they provide more calories and cause a greater rise in insulin than do the non-starchy vegetables like peppers, lettuce, spinach, and celery (which contains almost no starch at all). But on a spectrum of good and bad carbs, even the starchy vegetables and fruits, along with whole grains and legumes can have an important place in our diets compared with white flour, white rice, and all the highly processed foods made with those ingredients.
A couple more points about carbs, while we’re at it, to continue from what I began to explain above. Our bodies have a very limited ability to store glucose that is not needed immediately. The liver—and to an even more limited extent, the muscles—can store small amounts in the form of long starch-like molecules called glycogen. Stored glycogen is easily broken down to glucose in times of need. But as I explained above, glucose (and fructose) that is consumed in excess of what can be immediately used or converted to glycogen is converted to…fat!
Far from being a toxin, the carbohydrate glucose is absolutely required for life. But the massive amounts of carbohydrates many of us consume in the form of highly processed foods (sugar-sweetened drinks and cereals, candy, baked goods, chips and other snack foods, and even beer) are undoubtedly responsible for the negative health effects we now associate with eating too much sugar and starch. Why? First, because these excess carbs are readily converted to fat, and second, because oftentimes, we let highly processed high-carb foods crowd out their more vitamin-, mineral-, and fiber-rich counterparts from our plates.
So, as I hope you have gathered by now, almost all foods contain some carbohydrates. And the complex carbohydrate-containing foods--fruits, vegetables, grains, and legumes--in addition to providing the glucose and fiber we need, also provide essential vitamins, minerals, water, and even varying amounts of protein, in far greater quantities than do “refined” carbohydrate foods; like white breads, pasta, and rice!
If your head is swimming right now I understand: My husband’s head spun when I tried initially to explain it to him! So, let me try to explain it in lay-person terms. Most of us eat too many carbohydrates and keep hearing we need to cut down on them. But when you're looking to eliminating "carbs," make sure the foods you're limiting are the ones made from refined grains, like white breads, pasta, and rice (i.e. those that contain mostly simple carbs (the sucrose I mentioned above) and NOT fruits, vegetables, beans, lentils, and WHOLE grains, like whole-wheat flour. Oh, you can also eliminate unnecessary carbs by cutting back on candy, cake, cookies, pastries, and especially sugar-sweetened drinks like non-diet soda... Just don’t do it at the expense of those important vegetables and fruits! The bottom line is to cut foods with more empty calories!
How much carbs do we actually need to eat? Ideally, carbs should contribute about half of the energy (calories) we need. With the exception of fiber, the Recommended Dietary Allowance (RDA) for carbs is based on the amount research has shown our brains need to function and is also based on age and gender: for adults, the RDA is 130 grams per day. What does this mean in terms of actual food? Here is a short list of foods and their carb contents. The internet is teeming with much more complete lists.
Food Carbs (grams)
1 (1 ounce) slice of bread 10
½ cup cooked oatmeal 12-15
1 cup cooked rice or pasta 45
½ cup beans (like kidney, lentils, navy) 18-22
½ cup cooked corn 15
1 6-oz. potato (small) 40
Rather than focusing on that 130 gm, a much easier way to ensure you’re getting the right proportion of foods with healthy carbs is to imagine that each time you eat, your plate is divided into 4 quarters: 2 of those quarters should be filled with vegetables and fruits, another quarter should be grains, preferably mostly whole grains (like whole wheat bread and pasta, brown rice, quinoa…), and the other quarter should contain the foods that are richest in protein (meat, poultry, fish, cheese, eggs, even legumes, nuts, and nut butters)!
Fiber has its own recommended intakes: 38 grams per day for men 19 to 50 years of age (25 for women), and 30 grams per day for men 51 and over (21 for women). Most of us consume far too little fiber, and research suggests we need a wide variety of fiber-containing foods, so a fiber supplement is unlikely to fill the bill. Here are the fiber contents of some foods.
Quantities of Fiber in Some Commonly Eaten Foods
Food Fiber (grams*)
1 oz whole wheat bread** 1.9
1/3 cup bran buds cereal 11
1/2c whole wheat pasta, cooked 3.2
1/2 c Lentils 7.8
½ c Garbanzo beans 8.1
1 oz Peanuts 2.7
3 c popcorn 3.5
1 medium sweet potato w/skin 3.8
½ c artichoke hearts 7.2
1 medium green pepper 2.5
1 medium pear 3.1
½ c raspberries 4
*1 gram is about 1/30th of an ounce; ** a very thin slice!
Fats
Fat—or dietary fat—is found in all foods of animal origin (meat, fish, dairy foods, and eggs): Think of the white streaks in steak, those white lines you see in farm-raised salmon, the white blobs under the skin of chicken, butter, and heavy cream. But to all my vegan friends out there, don’t start cheering yet! Although not as visible, fat is also found in plant foods that are actual seeds—like corn, nuts, whole grains, sunflower and sesame seeds, legumes (peanuts, soy), coconut, avocado, and olives—and the oils pressed from those seeds that we use in cooking or to make salad dressing. Of all the nutrients, fats probably contribute the most to imparting foods’ unique—and tantalizing—flavors! Fat also has more than twice the calories per ounce or gram than carbohydrates or proteins, which may be why we assume fat makes us…well…fat! But the real question is, does it deserve a place on our plates?
For many years, researchers and nutritionists believed—based on the results of observational studies[1]—that one type of fat was like any other type of fat and that all fat was bad: in other words, that eating too much fat of any kind increased our risk for chronic disease—especially heart disease, stroke, and cancer. As research continues, our understanding of the risks associated with fat consumption appears to be getting more nuanced. We now know that some kinds of fat are essential. There is also some evidence that at least some kinds of fat may actually be cardioprotective, as I’ll explain further below.
Dietary fats can be divided into several different categories, based on their chemical structures, about which I will try to spare you the details! You’re welcome! The primary categories are saturated fats, unsaturated fats, and cholesterol (alcohol is also sort of a fat, but I won’t discuss it here).
To oversimplify, saturated fats are molecules that resemble long charm bracelets overcrowded with immovable charms, and unsaturated fats are long charm bracelets that still have lots of room for charms (just think of that Pandora® bracelet you got recently that only has two charms on it). This “crowding” or lack thereof, appears to be influential in how the saturated and unsaturated fats behave after we digest them--how they’re transported, where they’re stored, and what they’re used for. For these reasons, they have differing effects, both good and bad, on our long-term health.
Eating larger amounts of the more crowded—saturated—fats has been associated with overweight, high blood pressure, heart disease, strokes, and cancer, in studies of people who report what they ate and are then tracked over years. Saturated fats tend to be found almost entirely in the animal products we eat, including red meat, poultry, whole milk, and butter, although they are also plentiful in three plant products of note: coconut, palm oil, and palm kernel oil.
Unsaturated fats are further characterized by just how uncrowded they are: you may have heard terms like monounsaturated fat (for example olive oil) and polyunsaturated fat (for example, safflower oil).With the important exceptions I noted above, most fats found in plant foods are unsaturated fats.
At this point you may be asking yourself, “is this cholesterol I keep hearing about a charm on one of the bracelets, and if so, which one?” Well actually, cholesterol isn’t one of the charms at all: It’s a small molecule that looks very different from the saturated and unsaturated fats. Cholesterol is found only in animal products—notably eggs and shellfish—and for reasons we’ll discuss below has been inappropriately/confusingly targeted as a nutrition evil. Please be patient. I won’t forget about it!
In our own bodies, fat molecules actually play crucial roles: They’re the stuff our cell membranes are made of; they serve as protective insulation in the nervous system; they transport vitamins A, D, E, and K (referred to as fat-soluble vitamins); and they serve as a source of energy when carbs are scarce…but in excess, some fats clog up our arteries, and get stored in and around our vital organs (abdominal fat) and under our skin (subcutaneous fat). Fat is the form in which our bodies store excess calories. Our bodies can actually manufacture fat from carbs, proteins, and the fat we eat. So, since you may still keep hearing that you should eliminate fat from your diet, why should you consider fat a vital nutrient? Well, it provides energy—lots of it—and as we’ll soon see, there are certain essential fats we can’t make.
You might be feeling confused right now about whether the fat in our food just becomes the fat in our bodies, and if not, what’s the difference? Does that fat on the steak just get applied to my thighs? Not really. The fats we eat are disassembled slightly and then reassembled to be transported to where they’re needed, and then reconfigured again in the form of cell membranes, made into other important structures, or stored as fat. The unsaturated fats appear to play a role in binding and removing certain toxic substances from our bodies.
As I said above, with a couple of exceptions, our bodies can actually manufacture most of the fat molecules and all the cholesterol we need, from excess dietary carbs, fat, and even proteins. Those exceptions are the essential fatty acids. The essential fatty acids most familiar to most people are the omega-3 fatty acids: Omega-3 simply describes where the empty sites are on the fatty acid chain (“bracelet”). Omega-3 fatty acids are critical for brain and nervous-system development.
Now, I apologize in advance, but I need to get really technical right now regarding Omega-3’s because there are expensive over-the-counter supplements being sold that many of us do not need. Well, here we go. Alpha linolenic acid (ALA) is the omega-3 fatty acid found in plant foods (like canola oil, flax seeds, and walnuts). Our bodies can convert ALA to the two animal forms of omega-3 fatty acids, called Docosahexaenoic Acid (DHA) and Eicosapentaenoic Acid (EPA), that are vital for development and maintenance of the nervous system. But our bodies are not terribly efficient at that conversion. For those of us humans who consume animal products, especially salmon and other fatty fish, those products are the source of our DHA and EPA and generally supply all we need; however, strict vegetarians and vegans must rely on their bodies to convert ALA. People who avoid animal products must make sure to eat lots of dark leafy green vegetables, flax seeds and oil, soy beans, nuts, and other plant foods that supply ALA. Evidence has shown that taking over-the-counter omega-3 fatty acid supplements—like that fish oil that makes you burp—is not really beneficial. However, there appears to be one notable exception. Some recent evidence shows that a very high dose prescribed form of EPA may help prevent a certain form of heart disease.
There is also another essential fatty acid, omega-6 fatty acid or linoleic acid, which is plentiful in most edible seeds (especially corn), nuts, beans, and oils—so plentiful that in the US, we don’t worry about people’s intakes of this fatty acid, except some researchers believe that all those omega-6 fatty acids might actually crowd out our bodies’ ability to absorb ALA, DHA, and EPA, contributing to our bodies becoming deficient in those essential fatty acids. As more evidence comes to light, I will update this page or include it in a future blog.
As I mentioned above, a large body of evidence, almost entirely indirect observational evidence, has suggested that people who eat larger amounts of saturated fat (remember…the ones with the “crowded” chains, found mainly in animal products), particularly in the form of red meat, have a higher risk of chronic diseases like heart disease, stroke, and cancer. Among the plant foods we eat or use in cooking, coconut, palm oil, and palm kernel oil are the only ones that have any substantial amount of saturated fat. So far, we have no evidence that the saturated fat in these three foods is “healthier” than saturated fat from meat. Saturated fat “appears” to be saturated fat…period! In contrast, unsaturated fatty acids, eaten in the form of plants, meaning again, whole grains, beans, nuts, seeds, legumes, olives, and avocado, and in the form of fatty fish, have been associated with less risk of chronic disease. Do these foods actually protect us from disease, or is it just that when we eat more plant foods and fish, we tend to eat less meat and other animal foods? Again, based on indirect observational research (that is, studies where people are simply asked to describe what they ate and then tracked for months or years to see if they developed a disease), we actually have some reason to think plant foods and fatty fish are protective. But researchers aren’t sure whether it’s the unsaturated fats in these foods or some other nutrients (e.g., fiber, in the case of plants, vitamins, or minerals)? Because those empty sites on the unsaturated fatty acid “chains” can attach to certain chemicals that are thought to be toxic and remove them from the body, those fats might be playing a role in disease prevention! But no one really knows for sure: the evidence from studies of supplements like fish oil suggest that we need to eat whole foods, not just supplements or components of foods. And there are lots of other questions about fats to which we really don’t know the answers.
For example, some research—again, indirect—suggests that if all the plant fat we eat comes from palm or palm kernel oil (oils rich in saturated fat, often used to make highly processed snack foods) or even corn (a rich source of omega-6 fatty acids), rather than, say, olive oil and flax seed oil, we might as well just eat meat. But what if we switch entirely from butter to margarine? What if we consume potatoes only as French fries? What if we switch from eating lots of meat and poultry to lots of peanut butter and tofu? Or Whole wheat bread enriched with ground flax seeds? Is that really healthier than eating steak and cheese and butter? Evidence from studies in which people are randomly assigned to eat margarine or butter suggests a steady diet rich in margarine is no healthier than one laden with butter and maybe worse. Fried foods are associated with negative health consequences as well. Eating peanut butter and tofu in place of animal products is associated with less heart disease and longer life...but probably only if you also maintain a healthy weight. And finally, “trans” fats—a group of fats found almost solely in some commercial baked products but disappearing from the food scene—are now considered less healthy than any other fats. If your head is spinning about now, I understand (you should have seen my husband’s when we discussed this page!). The key is to strive to eat a well-balanced diet and get exercise, rather than rushing off to buy the latest supplement touted on the, “University of Google.”
But what about the keto diet, a diet that aspires to be nearly 100% fat, that has gained some press in supposedly helping with weight loss? This diet was actually developed to try to manage treatment-resistant seizures in young children. The evidence on whether it helps with weight loss long term is not great, and we know even less about how it might affect the likelihood of developing heart disease. Primarily because no one can really stay on it indefinitely. So many unknowns!
How much fat do we actually need? Remember that the only essential fatty acids we need to consume are the omega-3 fatty acids and the omega-6 fatty acids, as I mentioned above. The National Academy of Sciences Food and Nutrition Board, which establishes all nutrient guidelines for the US and Canada, sets a recommendation for the omega-3 fatty acid alpha-linolenic acid (ALA) (the plant source of this fatty acid – remember, you don’t get ALA from meat or fish!) of 1.6 and 1.1 g/d for men and women, respectively. Because what our bodies really need is the DHA and EPA that’s synthesized from the ALA (remember I mentioned that our bodies don’t make this conversion efficiently), individuals who eat meat or fish can more easily satisfy their daily requirement. So it’s imperative that those who avoid meat and fish, eat a well-balanced diet.
The Food and Nutrition board also sets a requirement for the omega-6 fatty acid, linoleic acid, of 17 and 12 grams per day for men and women, respectively. But deficiency of omega-6 fatty acids is unheard of in the United States: Even an ounce of potato chips provides a third of the day’s requirement!
Controversy surrounds whether consuming greater-than-recommended amounts of the omega-3 fatty acids in the form of fortified infant formula or fish oil capsules can help infant brain development and prevent long-term learning disabilities and chronic diseases in adults or whether we need to consume omega-3 fatty acids in their natural form—in foods. These questions have occupied the time of hundreds of scientists worldwide for decades, without definitive answers. However, the evidence is leaning toward getting our omega-3 fatty acids from real food, which has the added benefit of supplying lots of other nutrients as well. Here is a list of the omega-3 fatty acid contents of some foods. Remember that the daily requirements are for alpha linolenic acid (ALA); calculating the comparable amount of DHA and EPA remains challenging.
Quantities of Omega-3 Fatty Acids in Some Commonly Eaten Foods
Salmon (1 8-ounce serving, 6 ounces cooked): 1.2 gram DHA, 0.59 gm EPA
Sea bass (1 8-ounce serving, 6 ounces cooked): 0.5 gram DHA, 0.18 gram EPA
Shrimp (1 4-ounce serving): 0.1 gram DHA, 0.12 gram EPA
Walnuts (1 ounce): 2.5 grams ALA
Chia seeds (1 ounce): 5.1 grams Alpha linolenic acid (ALA)
Flax seeds (1 tablespoon, ground): 6.7 grams ALA
Edamame (1/2 cup): 0.3 gram ALA
Soybean oil (1 tablespoon): 0.9 gram ALA
Kale (1 cup chopped, cooked) 0.2 gram ALA
By now, you might be wondering what happened to little old cholesterol. I told you I wouldn’t forget about it! Cholesterol is a type of fat that is made in the liver by all animals and is a vital component of the membranes that surround our cells, not to mention that it is the building block for hormones like testosterone, estrogen, and cortisone. Our bodies make all the cholesterol we need and sometimes make excessive amounts, which tend to gather and lead to the blockage of blood vessels. For decades, we have known that people with heart disease tend to have higher levels of blood cholesterol than average. Because of that, dietary guidelines urged us to greatly reduce our intakes of cholesterol. And tremendous efforts went in to developing drugs that reduce our ability to make cholesterol (so-called statin drugs) and these drugs lower the chance of getting heart disease and strokes. Unfortunately, it has taken decades to resolve whether eating foods that are high in cholesterol—but not high in other fats—is unsafe. Although the current consensus is that cholesterol in foods is not the health issue it was once thought to be, the most recent Dietary Guidelines continued to equivocate about whether to limit cholesterol. The reason is that most—but not all—animal foods that are high in cholesterol are also high in saturated fats, which are the bigger concern. Eggs and shellfish are the exception. So, if you like eggs, enjoy them a few times a week—just go easy on the butter you use to cook them and the bacon and sausage you eat them with!!! And if you enjoy shellfish, dig in! Remember my earlier comment…moderation is the key! Happy eating!!!
[1] To learn about the different kinds of studies, see my blogs on how research gets done.
Protein
As a nutrient, protein often seems to have a halo around it, at least in the media. While we’re constantly being bombarded with alternating messages that sugar is toxic, that we should cut carbs, and that we should eat less animal fat, we never hear messages to eat less protein and are often being told why we should eat even more.
Most of the foods we eat contain some protein, although animal products (meat, fish, eggs, and dairy foods), beans, nuts, seeds, and whole grains are the best sources. Unlike carbs and fats, the proteins in foods aren’t easily divided into neat categories like complex and simple or saturated and unsaturated. Instead, one way researchers and nutritionists “categorize” food proteins is on a spectrum of lowest to highest quality. What makes a protein high in quality? To answer that question, it’s necessary to understand that there are thousands of different proteins in our bodies. Every single protein, from the ones that make up the bulk of our muscles to the ones that drive the millions of chemical reactions that keep all living things alive (called enzymes) to the ones that form your hair and fingernails—consist of very long chains made from unique sequences and combinations of 20 different subcomponents (links) called amino acids. So, for example, when we eat a piece of red meat or some tofu, the “proteins” within that food are broken down in our digestive systems into the individual amino acid “links” making up those proteins chains. These amino acids are then sent throughout the body where our different cells, tissues, and organs (e.g., muscles) reassemble those links into the proteins required for that specific cell, tissue or organ. In short, we never ingest a specific protein that is then sent in its totality to a specific place (which is why, for example, people who have diabetes can’t just pop an insulin pill: Insulin is a protein. It is also why bovine growth hormone can’t cause cancer in humans, and “BSH-free” milk is a waste of money).
Of those 20 kinds of amino acids, our bodies can synthesize 11 of them, or even interconvert them from one to another (e.g. asparagine into aspartic acid or glutamine into glutamic acid)! The other seven non-essentials are: alanine, arginine, , cysteine, glycine. proline, serine, and tyrosine. There’s a lot of other cool stuff going on with these in how they can interconvert and if you want to know more technical detail please email me your questions. However, for most people reading this page it’s simply important to know that these are called “non-essential” amino acids, because we aren’t required to get them from food – our bodies usually make enough on their own! The fact that our own bodies manufacture all the glutamic acid (aka glutamate) we need might also make you wonder how MSG (monosodium glutamate) could be poisonous: It’s not.
The other 9 amino acids—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—are called “essential” amino acids, because we can’t make them: We must eat foods that provide them. Foods vary in how well they (their proteins) can contribute to fulfilling that need for the essential amino acids. Cows, goats, and sheep, which are mammals like we are, have very similar protein structures to ours, so when you eat red meat or drink cow’s or goat’s milk, you’re getting basically all of the different amino acids you need. Poultry, eggs, and fish also provide pretty ideal proteins. However, the proteins in plants (which come in the form of whole grains, nuts, legumes, and other edible seeds and oils) are very different, and vary in the amounts of the essential amino acids they provide: Some may be high in one or even two, while being very low in others. The ability of a food to provide all the amino acids we need is what scientists mean, and you may have heard, by the term “protein quality. Why is this “quality” so important? Well, I’ll give you an example that should clarify it, but first, you might want to get up, stretch your legs, and even make a cup of tea before reading on, because I need to give you a small nutritional biochemistry lesson might take a few minutes to read and, um, digest!
Believe it or not, the cells throughout our body make anywhere from 10,000 to maybe a billion proteins—no one really knows! And every one of those protein types has a unique sequence of the amino acids. It is that sequence, ranging from a few to more typically hundreds or thousands of amino acids, that enables each protein to form the shape it needs to function, whether it’s a muscle protein that contracts to let us bend our knees, an antibody protein that must recognize a foreign invader, a receptor that serves as the entryway for a specific hormone, or an enzyme, of which there are hundreds, maybe thousands. Far from being random, these sequences have carefully evolved and are encoded in our genes. One tiny mistake in a gene (a mutation), which would result in an incorrect amino acid being added to a growing protein chain, could result in a disaster of minor to biblical proportions. Fortunately, dangerous gene mutations are relatively rare: two examples are the mutations that cause sickle cell anemia or cystic fibrosis.
Now that you understand something about how proteins are made in their correct sequences, I can proceed with my example, and for that I’ll use the essential amino acid “tryptophan.” The reason is that tryptophan is required by all mammals, not only as an amino acid that is essential to synthesize proteins, but also to synthesize serotonin. Serotonin is a neurotransmitter, i.e., it’s a chemical messenger that transmits signals from one part of the brain to other parts of the brain and the rest of the body, and is critical to our ability to feel pain, happiness, and probably to sleep . Ok, so suppose that for several weeks, you’ve been watching a lot of movies and your entire diet has consisted of popcorn and chocolate-covered raisins. Corn proteins are quite low in tryptophan. What happens when your body tries to synthesize new protein is that when it inevitably comes time to insert a molecule of tryptophan, the whole process comes to a dead stop when that tryptophan is missing; the protein synthetic machinery can’t just insert any random amino acid in place of the tryptophan, so the growing protein just falls off the protein synthesis mechanism and you don’t get the new protein! Eventually, a signal is sent to your muscles, and they start to break down to try to supply the needed tryptophan to synthesize important proteins, because the proteins in our muscles serve as a kind of emergency storage depot for amino acids when we’re not getting them from food. But we know from studies of starving people and even those on a very strict weight loss diet, that this can’t go on for long before a couple of really critical muscles—the diaphragm and heart—start to suffer serious damage. For this reason, the quality of a food’s protein is based on how well it keeps us from cannibalizing our own muscles—how well it can supply those essential amino acids in just the right proportions! In reality, determining the quality of a particular food source of protein is slightly more complicated: Some scientists have advocated taking into account how easily a food is digested, for example. And some scientists argue that the perfect protein might actually depend on our age: whether we’re infants (for whom the perfect protein is the stuff in breast milk), growing children, or adults…
But it should still come as no surprise that the quality of animal proteins tends to exceed the quality of plant proteins: Again, animals are made of pretty much the same stuff we are. Among the plant proteins, though, soy protein (as in tofu, tempeh, and edamame, soybeans themselves) is the highest quality protein. But if you follow a vegan or vegetarian diet, please don’t just run out and buy every soy product you can find, because not all soy products are good sources of protein. The processes used to refine some soy-based foods—such as soy bean oil and soy sauce— removes much or all of the protein. Foods that are good sources of soy protein include edamame, tofu, soy milk, and miso (although miso is insanely high in sodium and should be used sparingly).
What about the proteins in other plant foods like corn and other beans? Some plant proteins provide reasonable amounts of particular amino acids that are virtually absent from other plant proteins: For example, the corn scenario I mentioned above would make one’s body relatively low in tryptophan as well as lysine another critical amino acid!. Now some beans can provide the needed tryptophan, but may be relatively low in lysine). So, while corn would help you fill in some amino acids lacking in beans, you’d still need to get your lysine from somewhere else. So if you are following a strictly vegan diet, variety is key! Sticking with one or two “favorite” foods might not necessarily be the wisest idea!
As I mentioned earlier, when we consume protein, our digestive systems break it down to its component amino acids and transports them to the parts of the body that need them. To elaborate, as we use them, the proteins in our bodies—enzymes, protein hormones, even our muscles—are constantly “turning over,” that is being broken down and used up, and must be replaced by new ones. Every movement leads to the breakdown of small amounts of muscle; every breath, thought, meal eaten results in the use of thousands of enzyme molecules. Those all need to be replaced to avoid serious consequences. But is there any advantage to eating more than just enough protein to replace what we use? I’ll return to this below.
The recommended daily intake of protein is based on the amount needed to replenish what we use up and depends on our stage of development and our body weight: 0.8 grams per kg of body weight or a little less than 0.4 grams per pound for adults. Based on this estimate, a 200-pound man would require about 80 grams of protein a day. Another way of estimating our protein needs is that they should make up about 20% of our total calories. Here are some of the quantities of protein in typical servings of food:
The Amount of Protein in a Serving of Some Commonly Eaten Foods
One large egg: 6 grams of protein
A 4-ounce serving of chicken breast: 32 grams
An 8-ounce serving of salmon: 47 grams
One cup cow’s milk: 8 grams
One cup Greek yogurt: 12-20 grams
One ounce mozzarella cheese: 8 grams
One cup of diced tofu: 20 grams
One cup edamame, cooked: 17 grams
One cup soy milk: 8 grams
One cup pinto beans, cooked: 15 grams
One ounce almonds: 6 grams
Two tablespoons peanut butter (without sugar): 8 grams
One 2-ounce slice whole wheat bread: 8 grams
One cup cooked brown rice: 6 grams
One cup cooked oatmeal: 6 grams
Two ounces (uncooked) pasta: 8 grams
Now you can see that while it’s not too difficult to get enough protein if you eat a fairly balanced, varied diet, it can be a bit more challenging when plant foods are your only protein source: not impossible but just a bit more challenging than tossing a steak onto your plate. But there is an advantage to getting at least some of your protein from plants, as I will explain below.
Do any of us need to be concerned that the current recommendations on protein might be too low for our own personal needs? I’ve emphasized how important protein is but also how relatively easy it is to satisfy our protein requirements, even if you avoid all animal products. So if a little bit is good, is a lot a whole lot better? If you’re an athlete with long (hours), strenuous daily workouts that include a lot of weight-bearing exercise, you might need a little more protein to replenish the muscles you’re using and breaking down all day—an additional 20 or 30 grams. But if you’re just jogging or doing an hour on the treadmill or lifting weights an hour or so a day to bulk up (without taking ‘roids, of course), most of the evidence shows that taking extra protein might help little, if at all: Research shows that only relatively young men see increases in muscle mass from consuming extra protein and those can be small increases. Otherwise, all the extra calories will just get turned into and stored as fat. The one “non-athletic” group that might possibly benefit from eating more of their calories as protein (rather than as fat or carbs) are older adults, because aging brings about a steady loss of muscle protein, which can lead to loss of balance and a more sedentary lifestyle, which can in turn lead to even more loss of muscle. But this is still an active area of research, and evidence suggests that remaining active is just as important as eating extra protein, if not more so.
Is there a concern about eating too much protein? Because protein contains a lot of the element nitrogen, which our bodies need to make new amino acids as well as DNA and RNA, and because the kidneys filter and excrete any unneeded nitrogen when protein is broken down, it was conjectured at one time that excessive protein intake might strain the kidneys by forcing them to filter more amino acids than needed. Today, it appears this is a concern mainly for those who already have kidney disease. While not a common ailment in the past, kidney disease is now on the rise, largely because of the increase in Type 2 diabetes, which, if not controlled, leads to kidney failure and the need for dialysis and eventually kidney transplant. So the answer is that, as a result of this rise, for many people, eating considerably more than the daily requirement for protein may be worrisome. The absolute limit for safe intake is around 240 grams per day for a 150-pound person, but there is some concern for those who habitually consume upwards of about 140 grams per day (remember that an 8-ounce boneless chicken breast packs 64 grams).
Overconsuming protein can be a concern if the protein is in the form of red meat, poultry, or whole-milk dairy products like full-fat cheese: These foods come with excessive amounts of saturated fat (see my “fats” subsection for more information). And if the protein is in the form of processed meats like salami or bacon, they add a side dish of sodium and chemicals like nitrites that, in large amounts, have been implicated in increasing the risk for several chronic diseases. So as with all things, moderation is key!
Mounting evidence is showing that replacing even some of the animal protein in our diets with protein in the form of plant foods reduces our risk for heart disease. This evidence comes from studies where people told scientists what they tended to eat, which is always a bit chancy. And although the scientists made every effort to rule out the contribution of other healthy choices (for example, those who follow a vegan diet for religious reasons also tend not to smoke or consume alcohol), it’s still a little hard to tell whether the beneficial effects come from eating less saturated fat; eating more fiber, vitamins, minerals, and other seemingly important plant chemicals; or maybe a combination of both.
