The stated objective of genome research into obesity is to identify children at risk in a food-rich environment and to develop strategies to enhance satiety responsiveness. It’s important, however, to distinguish scientific terms that get confused in common vernacular.
Under the general meaning of “satisfying hunger,” satiation and satiety are used interchangeably. However, they mean different things.
“Satiation” refers to the end of desire to eat after a meal, and this can occur at any time after the onset of eating. Governed by hormones and stretch receptors in the stomach, satiation signals the brain the meal is over. “Satiety,” on the other hand, is a physical feeling of fullness that allows us to stop eating for a while. Ideally, satiety dwindles as nutrients diminish. When nutrients diminish, hunger returns.
The question for people eating in a modern food-rich environment is simple: What is the most effective strategy for satisfying hunger and preventing the overconsumption of calories that inevitably leads to obesity?
For the food processor creating a new product designed to satisfy hunger, the answer is not so simple. All macronutrients — proteins, fats and carbohydrates — have been linked to one or both of the distinct, though subjective, entities of satiation and satiety.
A clinical study published last year in the journal Obesity looked at the effectiveness of two high-fiber/low-calorie diets on satiety and weight loss over a four-week period. (Low-calorie diets alone often fail to meet fiber recommendations.) In the first, fiber was provided in the form of fruits, vegetables and whole grains. The second diet used beans as a primary source of fiber.
Both diets increased satiety while reducing calories. Both groups reported a decrease in hunger beyond baseline, even with a significant calorie reduction. This indicated the increased bulk of the diet was an important satiety factor.
A December 2013 study in the Journal of the American College of Nutrition, sponsored by PepsiCo on behalf of its Quaker Oats division, showed oatmeal was more effective than ready-to-eat cereal for satiety. The mechanism proposed appears to hold water, literally. Oatmeal is cooked in water, which allows the starch to fully gelatinize and the soluble fiber to fully hydrate, creating a viscous texture that presumably enhances satiety.
This result is consistent with the reported effect of oat porridge evaluated by the so-called Satiety Index. The Satiety Index evaluates satiety in comparison to white bread as the standard. Porridge is among the highest ranked foods by this measure.
The undisputed champion when it comes to the satiety index is the lowly and maligned boiled potato, a fact that tends to negate the independent effect of glycemic index when it comes to satiety. However there is another potential mechanism involved. The water-binding ability of starch and soluble fibers could have a specific effect on satiety.
Carbohydrates stimulate the release of insulin by the pancreas, driving not only glucose but large, neutral amino acids into muscle cells. This leaves tryptophan, the least abundant amino acid in foods, in a relatively higher proportion in blood. Tryptophan can more readily cross the blood-brain barrier and be converted to serotonin — the neurotransmitter associated with mood and appetite.
While the effect of protein on satiation and satiety is well known, increasing protein consumption beyond what is necessary to maintain nitrogen balance as part of a healthy diet does not appear to be justified, given the results of a recent article published last February in Cell Metabolism. The subjects, aged 50-65, who self-reported high-protein intake demonstrated a 75 percent increase in overall mortality, and a four-fold increase in cancer death risk during the 18-year period followed.
However, these associations were abolished or attenuated if the protein was plant-derived. For persons over 65, a high protein intake was associated with reduced cancer and overall mortality. However, there was a five-fold increase in diabetes mortality across all ages. The startling results argue for the use of varied plant proteins, whole grains, legumes, nuts and seeds — all of which are associated with satiety and healthy weight.