By: Dr. Caitlin Vonderohe
Professor Steven Simpson of the University of Sydney presented the keynote address entitled “Nutrient specific appetites and the ecology of diet balance” at the 14th International Digestive Physiology of the Pig Symposium in Brisbane, Australia. In this presentation he discussed his work in “Nutritional Geometry,” particularly the importance of nutritional balance for health, reproduction and growth in a multitude of species.
Organisms, ranging in complexity from slime molds, to insects, to humans, have specific appetites for protein, carbohydrate, fat, calcium and sodium. The benefit of nutrient specific appetites is the consumption of nutrients based on requirements typically ensures that other nutrients are brought “along for the ride,” or are also adequately consumed and absorbed. This phenomenon has been observed by multiple investigators in both domestic and wild species. For example, a wild baboon will consume various foods of various nutrient contents, but this diet, regardless of individual components, will have a consistent cumulative crude protein of 20%. Slime molds will similarly source nutrients to meet a consistent ratio of energy to protein for growth.
When an available diet is imbalanced, organisms will adjust their dietary intake to meet either their energy or protein requirement. Primates spare protein, regardless of energy intake. If a nonhuman primate or a human is offered a diet that is low in protein and high in fat and carbohydrates, that human or nonhuman primate will consume enough of that diet to meet their protein needs, even if they are consuming an excess of fat and carbohydrates. The extra energy intake is converted to adipose tissue. This is frequently observed in people when ultra-processed foods are readily available. People eat highly palatable, abundant, and affordable foods that are high in carbohydrates and fat but low in protein to meet their protein requirement, resulting in excessive fat deposition and obesity. Conversely, if a human or non-human primate is fed a high protein diet, they will eat less of that diet, resulting in lower energy intake and weight loss.
Professor Simpson moved on to show that, though tempting, a high protein diet is not necessarily the key to health and longevity. In a large mouse study, investigators titrated dietary carbohydrate and protein ratios to study health outcomes such as longevity, metabolic and molecular markers of aging, and glucose sensitivity. Mice on the low protein and high carbohydrate diets had the longest median lifespans, improved mitochondrial function, increased glucose sensitivity and longer telomeres (a marker of cellular aging) but were obese. On the other hand, mice fed higher protein diets had advantages in markers of reproduction and reproductive capability, indicating a potential nutritional trade-off between longevity and reproduction.
Branch chain amino acids (BCAAs) are used as a marker of metabolic disease in humans. Professor Simpson described a final study on the effect of differing ratios of dietary BCAAs on mouse longevity and other markers of health. Mice fed a 200% ratio of BCAAs to non-branch chain amino acids were hyper-obese and lived 10-13% less long than mice fed a diet with 20% BCAAs to non-branch chain amino acids. Upon further scrutiny and follow-up studies, investigators found that the mice fed excessive BCAAs were over-consuming food to meet their requirements for other amino acids, particularly threonine and tryptophan, eventually resulting in obesity. When the ratio of BCAA to non-BCAA was corrected with supplemental threonine and tryptophan, the mice no longer over-ate and had similar body composition to the control animals.
Professor Simpson concluded that nutrition has the power to help people and animals lose weight, live longer and have healthy offspring. However, nutrition cannot do all of these things at the same time, with the same diet. The more science reveals about the interactions between nutrition, metabolism and physiology, the greater opportunities nutritionists and physiologists have to balance diets for maximal effects.