by Jason Fung
On the other hand, if you are trying to lose weight, then you should eat less protein than the 0.61 gram per kilogram per day estimate. Overweight and obese people not only have more body fat but also an estimated 20 to 50 percent more protein than a lean person. Different types of protein loss need to happen along with fat loss—skin, connective tissue, capillaries, blood vessels, and so on. All this protein needs to be catabolized (burned up and not replaced). You often hear about how surgeons must remove 20 to 30 pounds of excess skin and tissue after significant weight loss. Yes, that’s all protein that should have been catabolized.
Some people argue that protein builds muscle. Hmm. Eating protein without exercise builds muscle? Right. Dream on. If that were true, we would not have an obesity epidemic; we’d have a muscle epidemic. Americans eat more protein than most of the rest of the world, and the cover of Time magazine has never posed the question, “Is America too muscular?” Although adequate protein is necessary for good health, more is not always better. Some of the antiaging benefits of calorie restriction are due to less protein but likely also less refined carbohydrates. However, too little protein may lead to sarcopenia and frailty. Longevity requires a happy medium.
Dietary protein, through mTOR, stops autophagy, which declines with age; the result is the accumulation of damaged molecules.8 The amino acid leucine, which is in virtually all proteins, is a key regulator of autophagy; when leucine levels in the bloodstream rise, autophagy quickly drops, and vice versa. Conversely, intermittent fasting promotes autophagy.
The role of leucine means that you don’t need to lower your protein intake much, if at all, to get the benefits of increased autophagy (although you might need to lower overall protein to get the benefits of reduced IGF-1). Decreased meal frequency, such as eating only once a day or eating only during a restricted feeding “window,” such as an eight-hour period daily, may activate autophagy without reducing calories or protein overall.
Longer periods of fasting, coupled with lower protein intake, have a pronounced antiaging effect through the renewal of immune system cells.9 Other diets that mimic fasting might have some benefit, too.10
Lower protein intake over a period of hours to days can have many benefits. Resuming normal protein intake then stimulates muscle to renew itself. This system of protein cycling could promote life extension while preventing muscle loss.
Based on these physiologic principles, a low-carbohydrate, adequate-protein diet would produce many of the benefits of calorie restriction. Carbohydrates, particularly refined carbs, stimulate both insulin and mTOR, which turns off autophagy. A diet low in carbohydrates and only moderate in protein would involve eating lots of natural fats, which are not to be feared. Dietary fat does not stimulate insulin, mTOR, or IGF-1. Indeed, early research confirmed that a high-fat, adequate protein, low-carb diet dramatically improved biomarkers of aging, such as improvements in body weight, leptin, fasting glucose, insulin, and triglycerides.11 As a side benefit, subjects lost an average of 8 kilograms (17.6 pounds) in body weight. Specific restriction of the dietary amino acid methionine decreased mitochondrial damage. The subjects were counseled to limit their protein intake to 1.0 gram per kilogram of lean body mass; those subjects who exercised were told to increase the quantity to 1.25 grams. Lose weight and increase longevity? Sounds like a plan.
Jordan Peterson, a professor at the University of Toronto and bestselling author, and his daughter, Mikhaila, have both followed in recent years a carnivorous diet, consisting of meat, salt, and little else. Mikhaila had been diagnosed with juvenile rheumatoid arthritis, depression, and idiopathic hypersomnia. All that disappeared when she switched to eating meat only. They eat 100 percent animal foods. Vegans, on the other hand, eat no animal products, so they eat 100 percent plant foods. Major food chains have added vegan choices including meatless burgers. Guinness, the famous Irish beer, stopped using fish bladders in its brewing process after more than 200 years. According to the newspaper the Guardian, we are witnessing the “unstoppable rise of veganism: how a fringe movement went mainstream.”1 Members of each group feel terrific on either all plant or all animal foods. Who is correct? Which proteins are optimal for health—animal or plant? What does the science tell us?
We often associate the word protein with animal foods. However, vegetables also contain protein in varying amounts. Tofu, chickpeas, lentils, beans, wheat (gluten is a protein), nuts, and seeds are sources of plant proteins. We rarely see serious protein deficiency in North America, except perhaps in alcoholics. So, a largely vegetarian diet is not necessarily deficient in protein. Instead, the main culprit that could lead to inadequate protein intake is the consumption of highly processed foodlike substances such as soda, candy, chips, and pretzels. These drinks and foods contain mostly carbohydrates and refined fats such as vegetable oils, and they’re generally very low in protein.
All plants contain protein because they need it for proper structure and function. Animals ultimately get their protein (essential amino acids, to be precise) from plants, either by eating them directly or by eating other animals that eat plants. Still, plant protein differs from animal protein in many ways that have significant health implications, particularly for aging and life span.
The Difference Between Plant and Animal Protein
The simple word protein gives little away of its complexity. Carbohydrates are chains of sugar molecules, sometimes long and sometimes short. Fats (triglycerides) consist of three chains of fatty acids linked to a glycerol molecule. Proteins, however, can be of virtually any size and composition and contain different amounts and types of amino acids. They range from two amino acids linked together to chains that stretch hundreds of amino acids long.
Plants must synthesize all of their necessary amino acids, whereas animals eat plants to obtain the essential amino acids they cannot produce themselves. Except in very limited amounts, humans do not store protein or amino acids. Small amounts of amino acids exist in our bloodstreams at all times due to normal turnover of protein. Old tissues can be broken down into component amino acids, which can be recycled into newly built proteins. Cells are continually being degraded and rebuilt to rejuvenate tissues. Red blood cells, for example, survive for only about three months before being replaced. Nerve cells (neurons) often live for decades, which is why nerve injuries heal so slowly. Skin cells are replaced every few days.
Protein, either from diet or breakdown of tissue, is used for two main purposes:
• To build (or rebuild) tissues
• To be burned or stored as fuel (glycogen or body fat)
Because of the many different proteins in our bodies, we require specific types of amino acids in the right quantities. Because the body can’t store amino acids, except in very limited amounts, we must eat the right amount and proportion of amino acids when we need them. This system seems precarious because nature does not email us a handy daily list of which proteins to eat. Anyway, most of the foods we want to eat (either animal or plant) might not be available at our convenience. During the turnover of proteins, most of the amino acid components can be recycled and used to build new proteins, so we don’t have to obtain all of them through diet alone.
Some proteins are easier for us to use than others. This concept is known as the biological value of proteins, and it’s expressed as a number from 0 to 100. A protein with a biological value of 100 contains all the amino acids in the right proportions for humans to use. Egg protein has a value of 100; gluten, the protein found in wheat, has a value of 64.
If you eat eggs, you can use 100 percent of its protein. If you eat wheat, you can use only 64 percent of its protein. Plant proteins generally have lower biological values than animal proteins because humans are biologically much closer to animals than plants. Plant proteins serve vastly different purposes than animal proteins, such as contributing to photosynthesis, and they have vastly different physiology. However, the generally lower protein content and biological value of plants do not necessari
ly mean that plant foods are not good sources of protein.
Protein Source
Bioavailability* Index
Whey protein isolate blends
100-159
Whey concentrate
104
Whole egg
100
Cow’s milk
91
Egg white
88
Fish
83
Beef
80
Chicken
79
Casein
77
Rice
74
Wheat
64
Soy
59
Beans
49
Peanuts
43
*Bioavailability is the amount of protein that is absorbed in the body.
Vegans eat only plant foods and rarely experience severe protein deficiency. However, even minor deficiencies can cause health problems, and vegetables might not provide adequate amounts of all of the proteins necessary for humans. For example, lack of dietary niacin, also known as vitamin B3, may cause pellagra, which can present as delusions, diarrhea, inflamed mucous membranes, and scaly skin sores. This disease was previously quite widespread across the southern United States, where corn was a staple food to the exclusion of much else. The native tribes had traditionally treated corn kernels with an alkaline solution known as lime water, or they sometimes used wood ash. This treatment removed much of the aflatoxins (toxins found in the mold) and also increased the availability of the niacin in the corn. When people throughout the United States adopted corn as a staple crop, they didn’t adopt the traditional preparation methods, which led to a pellagra epidemic. Lack of tryptophan, an amino acid, also can lead to pellagra because the body uses tryptophan to make niacin. In developed countries, pellagra is mostly a thing of the past.
Most animal proteins, like meat, eggs, milk, and cheese, are considered complete because they contain all nine essential amino acids. Most vegetables, by contrast, are not complete sources of protein. Eating a variety of vegetables is usually necessary to get all the essential proteins. The classic combination of rice and beans, for example, provides all the amino acids necessary for optimal health. Estimates suggest that people in the United States typically obtain about 70 percent of their protein from animal sources and 30 percent from plant sources.2 Is this the optimal mix? A great way to get healthy sources of whole food plant protein is by eating organic nuts—such as almonds, hazelnuts, or cashews—from a company like Organic Traditions (http://organictraditions.com).
Animal Proteins
Animal and plant proteins differ mainly in their amino acid composition. Animal proteins contain more of the three branched-chain amino acids (BCAAs)—leucine, isoleucine, and valine—as well as the sulfur-containing amino acids cysteine and methionine.
Bodybuilders and other athletes often take BCAA supplements to increase muscle growth. They activate mechanistic target of rapamycin (mTOR), the cellular engine of growth and aging, and increase insulin-like growth factor 1 (IGF-1), which is great for building muscle. However, if longevity is your goal, this might not be so great because the enhanced growth might mean a shorter life. In the next few sections, we cover several different types of animal proteins, including their advantages and disadvantages.
WHEY
During cheese production, the curds are removed from the liquid milk portion, which contains proteins called casein and whey. Cow’s milk contains approximately 20 percent whey protein, whereas human milk is about 60 percent whey protein. Whey contains a mixture of proteins, such as lactoglobulins and lactalbumin, which boost immunity and glutathione (an endogenous antioxidant). Whey also has displayed antiviral and antitumor effects.3
Undenatured whey has not been exposed to high heat and retains much of its original shape compared to the chemically processed whey often found in supplements. Studies in mice show that undenatured whey raises glutathione levels more than denatured whey4 and that this effect may be protective against cancer.5 Undenatured whey also enhances immune function.6
Protein Powder
Whey contains large amounts of the sulfur-containing amino acid cysteine, which is the critical rate-limiting factor in the production of glutathione, the body’s most important internal antioxidant. Whey can potentially ameliorate oxidative stress and may be especially important for the elderly.
Ryse Supplements (https://rysesupps.com) makes a unique “loaded protein” that contains whey protein, MCTs, and organic prebiotic fiber. This supplement is particularly beneficial because it acts more like a whole food than an isolated protein.
Cysteine
Diabetics have low levels of glutathione and higher levels of oxidative stress. Cysteine supplementation (using the supplement N-acetylcysteine, or NAC) restored glutathione levels and reduced oxidative stress.7
NAC supplementation also might be useful for other conditions, including bipolar depression,8 addiction, obsessive-compulsive disorders, and schizophrenia.9 Human immunodeficiency virus (HIV) causes a massive loss of sulfur, which depletes glutathione.10 Whey promotes weight gain and greater glutathione levels in HIV-positive individuals.11
Besides whey, the over-the-counter supplement NAC also supplies cysteine and thus replenishes glutathione. Cysteine itself is readily oxidized, which makes it difficult to store, but NAC does not oxidize, so it has a stable shelf life. During the metabolism of NAC, cysteine is liberated. NAC has a good safety profile, it’s inexpensive, and there’s even evidence that it can help people with chronic obstructive pulmonary disease (COPD) and influenza.12
Aging itself has been characterized as a “cysteine deficiency syndrome,” and provision of cysteine in the form of whey or NAC can largely alleviate the oxidative stress and inflammation of aging.13
BCAAs
Whey is an especially rich source of easily digested BCAAs, mainly leucine, which makes it popular with bodybuilders, who often take about 20 grams of whey after exercise. The increased blood leucine level stimulates mTOR-favoring muscle growth more than other proteins, like casein or soy. This stimulation of mTOR might be useful in sarcopenia (muscle wasting) and cachexia (pathological loss of both lean and fat tissue, most often seen in cancer patients).14 The high content of BCAAs in whey can overcome the anabolic resistance associated with aging. BCAAs also are used in treating liver cirrhosis.15 In mice, supplementation with BCAAs might increase life span, perhaps due to increased mitochondrial activity and muscle mass.16
CASEIN
The other 80 percent of the protein in cow’s milk is casein (Latin for “cheese”). In human milk, the percentage of casein varies from 20 to 45, depending on the stage of lactation. Until recently (in evolutionary terms), humans did not consume milk or milk products after weaning because lactose intolerance was almost universal in adults. Children have a lactose-metabolizing enzyme that would shut down after weaning. This changed about 5,000 years ago; this enzyme stayed active, so lactose tolerance began to spread. From that point, humans could drink milk from cows and other animals. Many people today, particularly from cultures that do not consume much dairy, are still lactose intolerant. Other people have allergies or intolerances (or both) to the proteins in cow’s milk. However, there also are subtler problems.
Whereas whey can increase fasting insulin levels, casein stimulates the production of IGF-1,17 which promotes muscle growth. However, overconsumption of casein may promote aging and cancer in animals,18 although in humans, casein is not a carcinogen.
Cheese contains large amounts of casein but also plenty of healthy fats, vitamin K, and calcium. Most population studies find that eating high-fat dairy products is associated with weight loss, less diabetes, and lower death rates from heart disease and cancer. But, as with everything, balance is the key. Eating more than half a pound of cheese per day would likely accelerate aging and cancer. The dose makes the poison.
MEAT
Meat is the quintess
ential animal protein that humans have eaten for millions of years. However, the meat you buy from the supermarket today is not the same as the wild game your ancestors ate. The wild game had about seven times less total fat, three times less saturated fat, more omega-3, and less omega-6. Most primates are only occasional meat eaters, whereas humans vary widely from no meat to 100 percent meat. Some scientists believe that meat-eating was closely linked to the development of bigger brains. Archaeologists find that most large mammal species became extinct soon after the arrival of humans, suggesting that early humans preferentially hunted them for meat. Meat contains mainly protein and fat but little to no carbohydrate; the combination of protein and fat might have been necessary for enhanced brain growth.
Approximately 95 percent of Americans eat meat. The health effects of meat consumption are controversial, which is surprising, given our long history of meat-eating and its prevalence. Since the ascendancy of the cholesterol theory of heart disease in the late 1950s, we’ve been urged to eat less meat due to its high saturated fat and cholesterol content. But the truth isn’t so simple. No large studies have ever found a link between eating saturated fat, cholesterol, or red meat and heart disease. The government has revised national dietary guidelines to state that dietary cholesterol presents no health problems.19
