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Most of my patients tell me that the typical question their friends or family members have about this plant-based diet is how you get enough protein with so few animal products. Many people are still tied to the myth that a diet needs animal products to be nutritionally sound. To add to the confusion, diet books and magazine articles promulgate the myth that more protein is favorable for weight loss and carbohydrates are unfavorable.

If you are overweight, you have consumed more calories than you have utilized. Micromanaging the percent of fat, protein, or carbohydrates you eat isn’t going to change the amount of calories much. You need to consume less calories. Therefore, almost all overweight individuals need to consume less protein, less fat, and fewer carbohydrates—the sources of calories. Don’t worry about not consuming enough. With the exception of anorexics, it is very rare to find an American deficient in fat, protein, or carbohydrates.

Inhabitants of modern Western societies generally consume more macronutrients, especially protein, than needed. Protein is ubiquitous; it is contained in all foods, not only animal products. It is almost impossible to consume too little protein, no matter what you eat, unless the diet is significantly deficient in calories and other nutrients as well. Protein deficiency is not a concern for anyone in the developed world. Americans already get too much protein, and it hurts us. When you eat a diet rich in green vegetables and beans, you are actually on a diet fairly high in protein because they are proteinrich foods. And of course when your diet is mostly plant protein, you get your protein packaged with protective fibers, antioxidants, and phytochemicals—a horse of a different color.

But should we carry around little pocket calculators and track everything we eat to make sure we don’t accumulate more than 10 percent of our calories from fat? Do we have to watch what we eat to make sure we get enough protein? The reality is that the precise ratio of these nutrients doesn’t matter much. What matters is that you are not deficient in any needed macronutrient, that you are not consuming excess calories or excess of anything else that may be harmful, and most importantly, that you meet all your micronutrient needs without overconsuming calories. Simply put, the goal of a healthy diet is to get the most micronutrients, both in amount and diversity, from the fewest calories. And fewer calories means less protein too. The real concern should be getting too much protein, not too little.

The focus on the importance of protein in the diet is one of the major reasons the American public has been led down the path to dietary suicide. We have equated protein with good nutrition and tend to believe that animal products, not vegetables and beans, are the most favorable source of protein. We bought a false bill of goods, and the dairy- and meat-heavy diet has brought forth an epidemic of heart attacks and cancers.

When we hear something over and over, starting when we’re young children, we accept it as true. For example, the myth that plant proteins are “incomplete” and need to be “complemented” for adequate protein is repeated over and over. All vegetables and grains contain all eight of the essential amino acids (as well as the twelve other nonessential ones), although some vegetables have higher or lower proportions of certain amino acids than others. When eaten in an amount to satisfy our caloric needs, however, a sufficient amount of all essential amino acids are provided. Because digestive secretions and sloughed-off mucosal cells are constantly recycled and reabsorbed, the amino acid composition in postprandial (after-meal) blood is remarkably complete in spite of shortterm irregularities in the dietary supply of amino acids.

In North America about 70 percent of dietary protein comes from animal foods. Worldwide, plants provide 84 percent of calories. It wasn’t until the 1950s that human protein requirement studies were even conducted. These studies demonstrated that adults require 20 to 35 grams of protein per day.

Today, the average American consumes 100 to 120 grams of protein per day, mostly in the form of animal products—much more than necessary. People who eat a vegetable-based diet have been found to consume 60 to 80 grams of protein a day, still well above the minimum requirement.

Advantages of Going Vegan or Very Close to Vegan

Even though eating an occasional small amount of animal product as flavoring or a condiment won’t likely have a major effect on your diabetes control, there are other beneficial reasons to going all, or almost all, the way to a vegan diet. The main reason is that, for many people with diabetes, even a relatively low amount of animal protein in the diet could raise a hormone called insulin-like growth factor 1 (IGF-1). This is the main reason I am restricting intake to only six ounces per week.

IGF-1 is one of the body’s important growth promoters in the womb and during childhood growth, but it also has anabolic (body-building) effects in adulthood. It is a hormone with a similar structure to insulin. The production of IGF-1 primarily takes place in the liver, and its production is stimulated by pituitary-derived growth hormone.

IGF-1 signaling is crucial for growth and development in childhood, but it promotes the aging process later in life. Reduced IGF-1 signaling is associated with enhanced life span.

There is a tremendous amount of evidence regarding the life-span-enhancing effect of lower levels of IGF-1, especially in adulthood. Centenarians are known to be exceptionally insulin sensitive, which may protect against the insulin-resistance-associated, age-related increase in blood glucose levels. Lower levels of IGF-1 are associated with enhanced insulin sensitivity and enhanced life span. This is critically important for people with diabetes or a tendency to develop diabetes, as higher levels of IGF-1 promote both diabetes and cardiovascular death from diabetes. The higher the biological value of the protein consumed, and the more of it consumed, the more IGF-1 produced. So the regular consumption of animal products is the most significant factor promoting IGF-1. Muscle tissue can produce its own IGF-1 in response to resistance exercise, but this does not raise systemic IGF-1 unless a diet rich in animal protein is consumed.

IGF-1 and Cancer

The largest concern about elevated IGF-1 from our modern diet is its link to cancer. Elevated hormone levels caused by the Western diet are thought to contribute to the high rates of cancer in the modern world—not just sex hormones, such as estrogen and testosterone, but insulin and IGF-1 as well. The connection between increased IGF-1 signaling and cancer has been known for many years —in fact, cancer drugs targeting the IGF-1 pathway began to be developed in the late 1990s, and over seventy clinical trials have begun since then, many with encouraging results. Because IGF-1 signaling plays a key role in tumor growth, reducing IGF-1 levels by dietary methods is now considered by most scientists studying this subject to be an effective cancer-prevention measure. IGF-1 signaling is involved in a number of processes relevant to tumor growth: proliferation, adhesion, migration, invasion, angiogenesis, and metastatic growth. A diet rich in antioxidants and phytochemicals results in reduced inflammation, oxidative stress, and IGF-1, which are critical to protecting against cancer and maximizing longevity.

Protein Intake Promotes IGF-1

The composition of protein and the amount consumed also modify IGF-1 levels. Protein that is rich in the full array of essential amino acids causes larger increases in IGF-1 compared to protein not as biologically complete. Plant sources of protein are less concentrated. They supply adequate protein, but not excessive amounts like animal products do, and the body needs to combine the amino acids for biological completeness, so they do not promote a surge in IGF-1 like animal proteins do. For example, milk and dairy products contribute to this excessive IGF-1 in circulation. In a meta-analysis of eight randomized controlled trials, circulating IGF-1 was found to be higher in milk-consuming groups compared to control groups.

HIGH-CIRCULATING IGF-1 LEVELS HAVE BEEN LINKED TO SEVERAL CANCERS

Breast Cancer

The European Prospective Investigation into Cancer and Nutrition study found that elevated IGF-1 levels were associated with a 40 percent increased risk for women over the age of fifty. In the Nurses’ Health Study, high IGF-1 levels were associated with a doubled risk of breast cancer in premenopausal women. Additional human studies, reviews of literature, and meta-analyses have also associated elevated IGF-1 levels with breast cancer.

Colorectal Cancer
Elevated IGF-1 levels are associated with colorectal cancer, and IGF-1 promotes the spread of colorectal cancer cells.

Prostate cancer
A 2009 meta-analysis of 42 studies concluded that elevated circulating IGF-1 is associated with increased risk of prostate cancer.

Other Cancers
Gynecological cancers
Multiple myeloma
Sarcomas
Renal carcinoma

The Calorie Restriction Society is a collection of individuals who believe that consuming fewer calories will lead to a longer life. A six-year study of members of this group found that their IGF-1 levels were not significantly different from control groups on a standard Western diet (of course, body fat, fasting insulin, and inflammation markers were markedly lower in the calorie-restricted group). The Calorie Restriction Society group members were consuming an average of 108 grams of protein per day, far more protein than necessary. This led the researchers to then compare IGF-1 levels in members of the Calorie Restriction Society to vegans who had been consuming a moderately protein- restricted diet, averaging 50 grams of protein per day for at least five years. (One 3.5- to 4- ounce serving of chicken supplies 25-28 grams of protein.) The calorie intake was greater in the vegan group, but protein intake was lower and IGF-1 levels were indeed much lower. This study cautions that overconsumption of protein, even when restricting calories, can keep IGF-1 levels elevated—to a point similar to those of typical Western eaters, who overconsume calories overall, blunting the potential of a longevity-inducing diet style. For example, many people eat egg whites believing that because they are almost pure protein and have no fat, they must be healthy. In truth, the high concentration of a biological protein makes egg whites disease promoting. Plant-based protein is much healthier.