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Why Nutrition Should be Lifespan-Flexible: Introduction to the Protein Leverage Hypothesis

We all want to live long, healthy lives. And many of us would like to do so while being thinner or stronger than we currently are. For years, people have debated over which food category contributes the most to obesity and diet-related diseases: fats or carbs? Does protein intake play a role, either in maintaining, gaining, or losing weight? Finally, a breakthrough was made by Drs. Raubenheimer and Simpson of the University of Sydney, as outlined in their 2020 book Eat Like the Animals. What they discovered could revolutionize the way we think about nutrition across our lifespan.

Simpson and Raubenheimer describe something known as the Protein Leverage Effect: across human history, we have evolved to require an ideal daily quantity of the amino acids found in protein. Our bodies have the ability to recognize, without conscious control, when this protein requirement has been met, and that is the point at which we feel full and no longer want to eat. Simpson and Raubenheimer analyzed two main categories which can constitute a diet—fats and carbs (grouped together) and protein. When carbohydrates and fats make up a greater proportion of the diet than protein, a greater amount of calories must be eaten to reach the same protein requirement target. If a person eats primarily protein, they will reach the target faster, feel full sooner, and have consumed less calories overall, leading to weight loss.

Given this finding, could this be a solution to what many consider an obesity epidemic impacting our nation? Should we all load up on meat, protein shakes, and tofu? Not so fast. A study done by Simpson and Raubenheimer on fruit flies found that, while high protein diets lead to weight loss and increase in reproductive function, they also lead to decreased lifespan. Conversely, high carbohydrate and fat diets may lead to weight gain, but they increase lifespan.

These trends make sense within the evolutionary framework of r- and K-selecting life histories. R-selecting species are ones which have high reproductive rates, large numbers of offspring within one reproductive season, minimal parental care, and short lifespans (e.g. rabbits or bacteria). K-selected species, on the other hand, have lower reproductive rates, live longer, and spend more effort caring for their small number of offspring (e.g. elephants or birds). From the perspective of evolution, with offspring production (and thus gene propagation) as the goal, there are two ways to maximize the chances of this happening: either live a short life, expending energy reproducing frequently in the hopes that some of the animal’s many offspring will survive, or, live a long life and reproduce periodically, ensuring the survival of each offspring. And thus, as biology frequently ensures, we are faced with a tradeoff.

What are we to do then? By choosing to eat more carbohydrates and fats, are we dooming ourselves to a population of long-lived but obese individuals? Or by eating more protein, a population of ripped and lean but short-lived people? To Simpson and Raubenheimer, there’s no need to worry. Their proposed solution is to allow for nutritional recommendations to be flexible throughout our lives. When we’re young, a more protein-heavy diet can increase reproductive function and help us to lose weight and stay lean. As we approach old age, we can shift our diets to being more carbohydrate heavy, allowing us to live longer. Overall, the Protein Leverage effect provides insight that can help us all to connect with our evolutionary roots and live more closely to the way Nature intended.


Work Cited

Raubenheimer, David, and Stephen J. Simpson. Eat like the Animals: What Nature Teaches Us about the Science of Healthy Eating. Mariner Books, 2021.

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