A new study has shown impressive results for a very low carbohydrate (or “ketogenic”) diet.
Participants in a new 8-week trial lost an average of nearly 15 pounds, and what’s more, the loss was especially concentrated in the uniquely dangerous fat that surrounds the liver and other organs. The very low carb dieters also retained skeletal muscle mass and improved their insulin sensitivity, all of which suggests a much-reduced risk for cardiometabolic disease. These results were better, across the board, than those in a control group following a standard low fat diet.
Writing in the journal Nutrition & Metabolism (available in full here as PDF), researchers from the University of Alabama at Birmingham present the results of their experiment pitting a very low carbohydrate diet (VLCD) against a standard low fat diet (LFD). Study participants were older adults (60-75 years) with obesity, a population very much at risk of cardiovascular and metabolic diseases.
Notably, the adults in the experiment were not told to cut calories, nor were they even told that they were participating in a weight loss study. Any weight loss therefore would likely have been a natural consequence of the dietary restrictions—“spontaneously restricted intake,” as the authors term it—rather than any intentional effort to cut calories.
Weight loss was by no means the only goal. The doctors put these patients through the works: dual-energy X-ray absorptiometry to precisely determine fat and lean mass; magnetic resonance imaging (MRI) to assess fat and muscle distribution; euglycemic hyperinsulinemic clamp to measure insulin sensitivity. This battery of tests represented a scrupulously thorough look into the metabolic and cardiovascular risk factors of the study participants.
The LFD group lost some fat, but the VLCD group lost 5 times as much fat by weight. The VLCD group also saw remarkable reductions in both intermuscular and visceral adipose tissue—two types of body fat that doctors identify as being especially harmful. This represented a dramatic body composition change in just 8 weeks, whereas the LFD group did not exhibit any such losses. Why did the VLCD group lose so much weight? They ate less. There is some evidence that a high-fat diet is naturally more satisfying, leading people to reduce their overall consumption without even thinking about it. A dietary survey taken midway through the experiment confirmed that the VLCD group had reduced calories much more the LFD group did.
One concern with rapid weight loss is the potential of muscle loss, especially among the elderly. While the VLCD group did lose some lean mass, this number is difficult to interpret due to the effects that a ketogenic diet can have on water retention. That’s why the researchers used an MRI. The scan showed that there was no loss of skeletal muscle in the thigh, suggesting that the diet may effectively preserve important muscle mass even while dieters eat at a significant caloric deficit. The researchers speculated that the details of ketogenic metabolism explain this effect.
Perhaps the most encouraging result is the “significant” increase in insulin sensitivity over the 8 weeks on a very low carbohydrate diet. The euglycemic hyperinsulinemic clamp used to measure insulin sensitivity is an intense procedure—after fasting, patients are hooked up to multiple catheters for several hours while their blood sugar is stabilized by infusions of both insulin and glucose. Most dietary studies don’t include it, for obvious reasons, which makes this study unusually valuable. The participants in the VLCD group exhibited statistically significant improvements in three different measures of insulin sensitivity. The LFD group showed no improvement in insulin sensitivity. Why is it important? Insulin resistance, the decline of insulin sensitivity, is the root of a bewildering number of diseases.
Lipid panels also showed good news for the very low carb dieters. After 8 weeks of dieting the participants showed major improvements in HDL and triglycerides, as well as modest improvement in LDL, results that would have put a smile on any cardiologist’s face.
It is worth noting that the dieters in the VLCD group were encouraged to limit saturated fat intake from red meats, and to otherwise emphasize healthy options among very low carb ingredients: unprocessed vegetables, nuts and nut butters, fresh fish, olive and coconut oils. Dieters in the LFD group were also encouraged to concentrate on minimally processed ingredients, a “high quality, healthful” diet in the words of the researchers. It’s no surprise that both groups experienced some health benefits. Any diet concentrating on whole ingredients, even one higher in carbohydrates, is likely to be an improvement over the standard American diet.
Speaking to Today’s Practitioner, lead author Dr. Amy Goss stated that very low carbohydrate diets were already known to be safe options, but that “this is the first study to demonstrate depletion of ‘metabolically harmful’ fat depots while preserving skeletal muscle during weight loss in response to a VLCD in older adults.”
These results will come as no surprise to our contributor Dr. Mariela Glandt, who has recently written an e-book that argues that one can very quickly improve metabolic health with a very low carbohydrate diet, and explains how to do it. The book is titled How to Eat in the Time of COVID-19, in reference to the fact that metabolic health is such an important factor in the outcomes of those patients unlucky enough to have been hospitalized with the novel coronavirus. This most recent study is just even more evidence that very low carbohydrate diets can rapidly improve metabolic and cardiovascular risk factors.