Study: Balanced high-fat diet improves body composition, inflammation

From the Winter 2015 edition of Vanderbilt Medicine Magazine

Photo by Robyn Mackenzie/veer.com

A diet designed for weight loss not only helps people shed unwanted pounds and keep them off, it also may reduce the risk of heart disease, diabetes and other degenerative conditions, in part by “turning down the heat” of chronic inflammation generated by excess adipose tissue (fat).

Surprisingly, it may not be necessary to avoid all higher fat foods or lose a great amount of weight to achieve these health benefits. That’s what Vanderbilt University researchers found in a recent clinical study.

In a paper published in 2014 in the journal Metabolism, Heidi Silver, Ph.D., R.D., Kevin Niswender, M.D., Ph.D., and their colleagues reported that consuming a balanced high fat diet improved body composition, inflammation and vascular function in 144 overweight women.

The women ate a diet consisting of one-third saturated fats (found in foods like cheese, margarine and meats), one-third monounsaturated fats (found in olive oil and nuts), and one-third polyunsaturated fats (found in fatty fish, safflower and corn oils, as well as nut butters).

After 16 weeks, fat mass decreased, lean mass (muscle) increased, and blood levels of inflammatory cytokines fell substantially. Blood pressure also lowered significantly.

“Although the long-term effects have not yet been determined, the practicality of this approach offers a readily adoptable dietary strategy that not only results in weight loss, but also has the potential to improve cardiometabolic health,” Silver and her colleagues concluded.

Jennifer Gilbert and Andrea Hedley-Williams weren’t out to reduce inflammation when they signed up for the clinical trial in the Vanderbilt Center for Human Nutrition in 2011. They were mainly trying to find a readily adoptable weight-loss plan that wouldn’t make them feel deprived.

Gilbert, systems support coordinator at the Vanderbilt Clinical Staffing Resource Center, said she lost weight and her cholesterol dropped while on the study.

But the biggest change was her approach to food. “I focus on eating more whole, healthy foods. I don’t avoid … fats the way I did,” she said. “And my weight has been stable.”

Hedley-Williams, a Vanderbilt audiologist, said the allowance of fat in every meal surprised her, and helped her stick with the regimen—especially when she could prepare dinner that “everybody in the family could eat.”

There was another surprise. Before she started the study, Hedley-Williams thought she was pretty healthy. That perception changed after a few weeks, she said, when “I realized how much better I felt.”

This may not be the case for every weight-loss plan, however. In fact, some approaches to dieting—especially “yo-yo” dieting—may actually do more harm than good.

In a 2013 Vanderbilt study conducted in mice, Alyssa Hasty, Ph.D., and colleagues reported that repeated cycling between standard high- and low-fat diets increased the numbers of certain “T” white blood cells and the expression of pro-inflammatory factors in adipose tissue.

These weight-cycled mice also had decreased systemic glucose tolerance and impaired adipose tissue insulin sensitivity compared to mice that gained weight but did not “yo-yo” between high- and low-fat diets. This suggests that an exaggerated immune response in adipose tissue may contribute to metabolic dysfunction during weight cycling.

Another Vanderbilt study found that obesity-associated inflammation may affect even the brain. Mice fed a standard high-fat diet became obese and had a 30-percent increase in the number of fluorescently-labeled immune cells in the central nervous system compared to mice fed a standard control diet.

The findings suggest that peripheral immune cells can be recruited to the central nervous system and may contribute to the inflammatory response and the pathophysiology of obesity.

Beyond the amount of fat, a critical difference between the human and mouse studies may be the proportional balancing of the type of fat being consumed.