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Does being insulin resistant affect weight loss on a low-fat or low-carb diet?

Weight loss is not a simple issue. The impact of a diet could be influenced by whether or not you’re insulin resistant, as examined by this one-year trial of a low-fat versus low-carb diet.

Study under review: Effects of diet composition on weight loss, metabolic factors and biomarkers in a 1-year weight loss intervention in obese women examined by baseline insulin resistance status

Introduction

Obesity has recently been called[1] a “single house for many evils” based on evidence that it increases the risk for numerous comorbidities, including cardiovascular disease, cancer, and diabetes. One proposed explanation[2] for the link between obesity and other metabolic diseases is that obesity leads to chronic inflammation in some people, which in turn leads to a dysregulation of insulin signaling, also known as insulin resistance.

Insulin resistance has widespread effects on health and is the hallmark[3] of metabolic syndrome and type 2 diabetes. Weight loss is a well-established method of restoring insulin sensitivity among people with obesity and insulin resistance. Several trials have shown that very low-calorie diets and rapid weight loss are able to restore insulin sensitivity and possibly even reverse type 2 diabetes. Of course, a very-low calorie diet (less than 1000 calories) is not sustainable over the long term.

Under more modest levels of caloric restriction, weight loss is achievable with a variety of macronutrient (protein, carbohydrate, and fat) intakes. This was discussed in “The best diet is the one you can stick to” in the first issue of the ERD, where 11 popular name-brand diets were compared for their ability to produce weight loss among individuals with obesity. The results showed that while there were some differences between diets, overall any diet was better than no diet at all.

Still, the question remains as to what the optimal macronutrient distribution for a weight loss diet is. Two previous short-term[4] studies have suggested that insulin resistance may predict which macronutrient distribution is most beneficial. Specifically, these two studies showed that insulin resistant individuals lose more weight on a low-carbohydrate diet, as opposed to a low-fat diet. However, a more recent study with a stronger methodological design did not support these findings.

Aside from macronutrients, the actual foods included in the diet may influence weight loss. For instance, “Blast from the past: a paleo solution for type 2 diabetes” from ERD #8 explored a study that compared two diets of equal calorie and macronutrient content, with the difference being what foods supplied them. One group ate an American Dietetic Association diet while the other ate a Paleo diet. Although both groups lost a similar amount of weight and showed similar improvements in insulin sensitivity (again suggesting that weight loss is the most important), the paleo group showed superior benefits for changes in blood lipids and glycemic control.

In this regard, walnuts may be of interest because of their ability to reduce[5] inflammatory markers and blood lipids without significantly affecting weight, despite contributing a substantial number of calories to the diet. And more directly, walnuts may also be of interest because the study under review was partially funded by the California Walnut Commission. Nonetheless, long-term walnut trials are still necessary to investigate if the previously identified benefits are merely transient.

The current study sought to examine the effect of three diets (low-carb, low-carb plus walnuts, or high-carb) on weight loss and other markers of health in overweight or obese women over a one-year period and determine whether baseline insulin resistance influenced the effectiveness of the interventions.

Obesity greatly increases the probability of suffering from insulin resistance, which in turn serves as a hallmark of metabolic syndrome and type 2 diabetes. Weight loss is known to restore insulin sensitivity, but the optimal macronutrient distribution of a weight loss diet has not been established. Certain foods, such as walnuts, may also have a beneficial impact on health. The current study sought to compare three diets differing in macronutrient composition and the amount of walnuts in the diet on their ability to produce weight loss over a one-year intervention. This study also investigated whether baseline insulin resistance influenced any outcomes.

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