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.
The results from Dr. Goss’s study are intriguing, but I’m not completely sold on them. Some issues that come to mind include:
-Although there is a redistribution of fat to be stored subcutaneously, is a high fat diet really going to have that great of an impact when it comes to reducing the “greater health concerns ” posed by visceral and intramuscular fat storage if individuals are still overweight?
-If there is a significant reduction in greater health concerns when sites for fat storage are manipulated, does this imply a correlation with increased fitness and quality of life, and decreased risk for comorbidities?
-Overweight and obese individuals have a greater proliferation of adipose tissue due to both hypertrophy and then hyperplasia of fat cells. Once fat is able to be redistributed to subcutaneous sites for storage, thus reducing the hypertrophy of fat cells in the visceral and intramuscular adipose tissue sites, what’s to say that a diet high in fat would not eventually result in increasing overall fat storage at these sites due to the already increased density of fat cells capable of storing this excess dietary fat at these sites?
-What is the timeline and adherence rate for this type of diet? Is it meant to be a transient solution or a lifetime commitment?
In light of all of these questions, including the limitations posed in others’ comments, it is clear that more research is needed. However, these findings do pose some interesting implications for fighting the overweight and obesity epidemic in the United States.
Great summary on the body fat distribution and Dr. Gross research interest. I also find it interesting that different people respond to carbohydrates and insulin in different ways. Knowing this information serves as a great resource to have in our toolboxes as we interact within our communities or when targeting some specific populations, in possible diet interventions. Especially as about 36.5 % of US adults are considered obese (CDC Statistics). Obesity is a risk factor for heart disease, stroke, type 3 diabetes and some forms of cancer. Being able to provide more accurate or more advantageous recommendations would help combat this epidemic.
Very interesting discussion on this topic. It is not widely known or discussed that insulin secretion and levels vary from person to person. With that in mind, the results of the study make sense. Those that decrease the amount of carbohydrates in their diet will lower their the amount of insulin they produce. This will result less blocking of fat burning, and decrease the amount of lipogensis, leading to a decrease in the amount of fat that is being stored throughout the body. The one problem that I did see with this study was the population and CHO GI levels between the groups. The population that was studied was one that was already at an increased risk for visceral fat production. This predisposition makes it difficult to translate the results to other populations. Additionally, those in the experimental group were consuming CHOs that were lower on the GI than the control group. The problem with this is that those CHOs that are higher on the GI cause a greater spike in insulin and help to promote fat storage. It could be possible that the results were statistically significant because of this difference. Future studies should look at a more general population, and have similar CHOs that are being consumed.
HMR49592,
Interesting write up, I never thought about the fact that insulin secretion rates vary from person to person. The research by Dr. Goss stated that many studies show reduced carbohydrate and higher fat diets are beneficial for promoting optimal body composition; it is interesting they only reduced the amount of carbs in her study from 55% to 41% and saw these results. I looked further into the study and it appears that the lower CHO diet actually received a slower digesting carb verses the higher CHO diet, “The glycemic index of the standard diet was approximately 60, whereas that of the lower-CHO diet was approximately 50” (Gower et al., 2013). It is well known that quicker digesting carbs spike insulin levels and promote fat storage so I wonder if the results would’ve been the same if both diets were given the slower digesting carbs. I agree that additional studies are needed before practitioners change dietary recommendations for obese individuals.