Dr. Amy Goss of the University of Alabama Birmingham studies the effects of macronutrient manipulation (or manipulations of the proportion of carbohydrate, fat, and protein in the diet) on body fat distribution and metabolic health in adults with obesity.
A quick note on body fat distribution: body fat can be distributed under the skin (subcutaneously), around the organs (viscerally), and in muscle (intermuscular). Visceral and intermuscular fat pose greater health concerns than subcutaneous fat. Dr. Goss’ work on many studies has shown that a reduced carbohydrate and higher fat diet results in a more optimal body composition and lower risk for type II diabetes in obese individuals.
When carbohydrates are ingested, the body secretes the hormone insulin. Insulin blocks fat burning and stimulates lipogenesis (fat synthesis) in the liver. Not all individuals produce the same amount of insulin in response to the same amount of carbohydrates, however. For example, African Americans secrete 2-3 times the insulin to the same amount of glucose as Caucasian individuals. Because some individuals are prone to excessive insulin secretion and subsequent fat accumulation, they may respond better to a lower carbohydrate diet.
Dr. Goss conducted a macronutrient manipulation diet study in women with polycystic ovary syndrome (PCOS). She used this population because patients with PCOS are at increased risk for visceral fat accumulation, which can cause resistance to insulin, and high insulin secretion. She tested a low carbohydrate high fat diet in these women and found that they had a selective depletion of their visceral and intermuscular fat without overall weight loss, retention of muscle mass, and improved metabolic outcomes for type II diabetes when compared to controls on a higher carbohydrate low fat diet. The women also had improved blood lipid values from baseline on the low carbohydrate high fat diet.
The potential impact of these findings is a change in the dietary recommendations given to obese individuals with high levels of visceral fat. The evidence from Dr. Goss’ work suggest that a low carbohydrate high fat diet may have beneficial body fat redistribution effects that help patients lower their risk for insulin resistance and type II diabetes. Pending further corroboration, practitioners could use this information to adjust their recommendations for obese individuals to strive for a diet higher in healthy fats (such as olive oil, avocado, nuts) and lower in carbohydrates. The fascinating thing to me is how different people respond to carbohydrates and insulin in different ways. The findings of this study and others conducted by Dr. Goss point to the idea that blanket recommendations, such as the low fat recommendations from the Dietary Guidelines for Americans, may not be ideal for everyone in the population.