High-Protein Diets: Too Much of a Good Thing?

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Standing before a vessel of simmering water, Dr. William Ja, of The Scripps Research Institute, carefully follows a recipe. To the steaming water, he adds cornmeal, yeast, sugar, and a little agar then stirs until the mixture thickens. With steady and quick movements, he scoops the hot meal into clear glass bottles where it cools. You would think that nearby flies would be shooed away, but in the Ja lab, flies are invited into the bottles. The sweet, yeasty meal has been made for them.

William “Bill” Ja studies fruit flies to research the affects of diet on aging and longevity. He believes that “flies have long served as good models for mammals.” His recent research on flies has shown that a high protein diet can actually shorten their lives. Similar research findings have been found independently through Kwang Pum Lee, a professor at The University of Sydney, Australia; Stephen J. Simpson, also a professor at The University of Sydney, Australia; and Valter D. Longo, a professor from The Davis School of Gerontology at the University of Southern California. These scientists agree: the length of an organism’s life can be shortened by eating too much protein.

It seems ironic that we can eat too much protein when our bodies are composed mostly of protein. Hair, skin, muscles, organs are all basically protein-based parts of our biological machines. And as with any machine, it wears down through constant use. To counter this wear, we need to consume protein to rebuild and restore any loss. However, it appears that we don’t need a lot of protein for restoration.

According to the Centers of Disease Control and Prevention (CDC) a complete restoration for most of us can be achieved by eating as little as 10% of our daily caloric intake in the form of protein, which, for the average adult consuming 2000 calories per day, is about 50 grams per day (50 grams of animal-derived protein is about 2 eggs and a 4 ounce chicken breast, while 50 grams of plant-based protein is about 1 cup of oatmeal, 1 cup of soy milk, 2 slices Whole Wheat Bread, 1 cup of vegan baked beans, 1 cup of broccoli, 1 cup of brown rice, 2 Tbsp of almonds, 2 Tbsp of peanut butter and 6 crackers). So, if we eat more protein than we need, we create excess protein, and through a complicated process, excess protein can cause a wave of cell damaging free radicals.

Free radicals are molecules that carry an imbalance in their atomic structures: specifically they need an electron to regain a balanced state. To get this missing electron, free radicals will tear it from any molecule nearby, including protein molecules. When free radicals attack protein, it becomes oxidized protein. Oxidized protein is damaged protein.

Because our cells are made of protein, they too can become damaged through oxidation, the results of which may lead to heart disease, cancer, and diabetes. According to these researchers, if we constantly ingest more protein than we need, a lifespan shortened by disease may be in store for us.

Kwang Pum Lee, reporting his research results in the peer-reviewed Proceedings of the National Academy of Sciences, fed fruit flies a variety of meals with different ratios of proteins and carbohydrates, namely 1:2, 1:4, and 1:16, (the 1s on the left side of the colon represent 1 calorie of protein, while the 2, 4, and 16 on the right side of the colon represent calories of carbohydrates). When Lee fed his fruit flies high protein diets, the 1:2 and 1:4 ratios, their median life span was 25.5 days and 35.9 days, respectively. When Lee fed a third group a low protein, 1:16 diet, the flies achieved a median life span of 56.7 days.

Bill Ja, reporting in the journal Experimental Gerontology, repeated close variations of Lee’s experiments with similar results. Bill also found that a low protein, 1:16 diet, achieved the longest lifespan. According to Bill Ja, “the high carb ratio diet is indeed better” for longevity.

Stephen Simpson, publishing in the peer-reviewed journal Cell Metabolism, arrived at similar results, but with mice. He fed 858 mice one of 25 diets that differed in their ratios of protein, carbohydrate, and fat content. The interactions between the nutrients were complicated. To help penetrate the complexity, Stephen utilized Geometric Framework (GF) – a statistical tool that made it possible “to disentangle the individual and interactive influences of multiple nutrients.”

By applying GF to the interactions between proteins, carbohydrates, and fats, Stephen discovered: “the longest median survival occurred in cohorts of mice on the lowest ratio diets, and there was a clear correlation between the ratio and lifespan. Median lifespan increased from about 95 to 125 weeks (approximately 30%) as the protein-to-carbohydrate ratio decreased.” Stephen concluded that “lifespan was greatest for animals whose intakes were low in protein and high in carbohydrate.”

The results obtained by the researcher, Valter D. Longo, who also published in Cell Metabolism, agreed with the preceding studies, except this time humans were the focus. Valter studied the diets of 6,381 adults ages 50 and over. The participants were part of the largest nutrition survey in the United States, the NHANES III. The size and scope of the survey gave Valter the statistical power to confidently say that people “aged 50–65 reporting high protein intake had a 75% increase in overall mortality and a 4-fold increase in cancer death risk.” Dr. Longo defined a high protein diet as a diet that consisted of eating 20% or more of one’s daily caloric intake in the form of protein.

To demonstrate the complexity of nutrition, Valter also found that people over the age of 65 actually do better on a high protein diet as more protein seems to help counter the natural frailty that occurs with older bodies. By eating extra protein, an elderly person can build bodily reserves to help weather the storms of age-related diseases. For adults 65 and younger, eating 20% or more of daily caloric consumption in protein appears, however, to stress bodies that are already fine tuned for optimal health by virtue of being youthful and in the prime of life.

It’s actually pretty easy to eat over 20% of daily caloric consumption in protein, especially with protein rich animal-based proteins. 20% of daily caloric consumption in protein for the average diet that would be over 100 grams of protein per day. 100 grams of protein in a day would look like this: 2 eggs (25g) for breakfast, 4 ounces of chicken breast for lunch (25g), and a 6 ounce steak (50g) for dinner. Even if we switched out the steak for 4 ounces of turkey or fish for dinner, we would still be at 95 grams of protein for the day. Throw in a cup of ice cream (because we were so good) to add another 5 grams would again make an even 100 grams for a high protein day.

According to these researchers a high protein diet, for most of us, appears to be too much of a good thing. So, what can we do about it? The simplest thing would be to eat less meat. According to the American Heart Association, nuts, greens, and beans and many other plant-based based protein sources can adequately fill our daily protein needs and, according to Valter Longo, plant-based protein actually appears to be healthier than meat-based protein. When controlling for the effect of plant-based protein, he found there was no change in the association between plant-based protein intake and mortality, which indicated to him “that high levels of animal proteins promote mortality.” Valter goes on to conclude that “a diet in which plant-based nutrients represent the majority of the food intake is likely to maximize health benefits in all age groups.”

So while most of us aren’t ready to chuck our ground chuck to pursue a vegan diet, it may be worth our time to pay attention to the latest discoveries in nutrition research. It’s also worth mentioning that the presented researchers are part of the same broad intellectual query started in the 1940s when it was discovered that by eating a minimal amount of calories per day, lab animals lived longer. Recent refinements to the theory have pointed to protein restriction as the life extending factor, not calorie or even carbohydrate restriction. Indeed, they agree more years will probably be granted to those rebellious folks who eschew high protein, low carbohydrate diets for low protein, high carbohydrate options, at least until they’re 65 and older.


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