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
Obesity has recently been called 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 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 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 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 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.
Other Articles in Issue #24 (October 2016)
Can vitamin D-crease pain?
Pain involves the nervous and immune systems, among others, so it can be tough to address through supplementation. Vitamin D's multitude of roles hint at its possible use as a pain treatment.
Interview: Josh Mitteldorf, PhD
Josh is well-known in the life-extension community, for looking deep into the literature and connecting the dots. We'll get his take on some interesting longevity-related topics. After 30 years wandering in the plasma physics of extragalactic radio sources, Mitteldorf came to the study of aging in 1996 to correct a fundamental error in the foundations of evolutionary theory. After 20 years, the revolution in biological concept of aging that he initiated is only now coming to fruition
When nitrate supplementation doesn’t involve supplements
We've covered several nitrate supplementation studies in previous ERDs. This trial is unique in that it studied the impact of a nitrate-rich diet on exercise performance.
Eat a day, skip a day?
Typical dieting can be a chore. An alternative is to eat less (or not at all) during certain time periods, otherwise known as fasting. This is the first trial to compare regular calorie restriction to alternate-day fasting.
The high cost of high heat cooking
The delicious browning and crusting of steak or chicken could also be harmful. This one-year long randomized trial looked at high-heat cooking versus gentler cooking, and its impact on insulin resistance.
Interview: Courtney Silverthorn, PhD
Are you in the life sciences, but not sure if you want to work in a lab? Courtney is uniquely qualified to give advice about this.
Examining the potential for edible sunscreen
Phytochemicals in plants are well known to have positive effects on chronic conditions, such as heart disease and cancer. But certain ones could also help you avoid ... sunburn.