Study under review: Effects of carbohydrate quantity and glycemic index on resting metabolic rate and body composition during weight loss
One of the biggest struggles for people who have lost weight is trying to keep it off. Weight regain after an initial period of loss is a highly common occurrence among dieters. While there are different reasons for this weight gain, a potential contributor may be the metabolic adaptation to weight loss itself. As weight loss occurs, a person will be physically moving around less mass, and therefore expending less energy. But these periods of weight loss can induce reductions in metabolic rate above and beyond what can be attributed to the weight loss alone. This is known as adaptive thermogenesis. Resting metabolic rate (RMR) is a component of energy expenditure that plays a role in adaptive thermogenesis. RMR is the amount of energy your body expends during a state of rest to keep all your organs and bodily systems functioning and, in most people, it is the biggest contributor to total daily energy expenditure.
It is plausible that dietary factors could help to prevent these reductions in RMR during weight loss. One area of research has examined carbohydrate quantity and glycemic index (GI) as a potential strategy to prevent RMR decreases. The glycemic index is a measure of how much a food will raise your blood sugar. To date, the research has been somewhat equivocal. Some studies have shown benefits for low-GI diets in terms of preserving RMR, but these studies did not match protein intake between intervention groups, which can confound the results. Other studies have shown no weight loss difference or significant changes in RMR between diets that altered both carbohydrate content and GI level.
This study aims to further examine the effects of dietary carbohydrate content and GI on RMR adaptations and changes in body composition during and following weight loss. By isolating both the carbohydrate content and GI level in a diet, we can better tease out if either of these variables may have an RMR preserving effect. Additionally, it is not known if diets very high in carbohydrate (greater than 65%) could attenuate these outcomes. The researchers conducting this study examined four types of diets in an effort to determine their ability to attenuate reductions in RMR.
Resting metabolic rate (RMR) can become depressed during and after weight loss. It has been hypothesized that this decrease in RMR could play a role in weight regain. The effects of dietary carbohydrate content and glycemic index to preserve RMR are not well known. This trial examines four diets varying in GI and carbohydrate content to determine their influence on RMR during and after weight loss.
Other Articles in Issue #14 (December 2015)
Investigating vitamin D as a performance enhancer
Having sufficient vitamin D levels has been associated with better muscle recovery. This trial not only looks at the question of causality, but also addresses some potential mechanisms of vitamin D’s benefit for exercise.
Trans fats: “natural” might not mean “healthy”
In the nutrition community, a common message has been that artificial trans fats are bad, however natural trans fats are not only okay but beneficial. This trial on blood lipids puts that to the test.
High versus low fat diets for insulin sensitivity
More body weight means more risk for metabolic syndrome. But the question of whether more fat (and especially saturated fat) impacts insulin sensitivity hasn’t been adequately addressed until now.
Exercise, with a (tart) cherry on top!
Berries have burst onto the research scene in recent years. Tart cherries have shown some of the most promise in certain areas, leading to this study of powdered tart cherry on exercise recovery.
Interview: Dan Pardi MS PhD(c)
Dan Pardi is an entrepreneur and researcher whose life’s work is centered on how to facilitate health behaviors in others.
Root rage: The impact of ashwagandha on muscle
So called “adaptogens” like ashwagandha are typically studied for stress-easing potential. A randomized trial looked into this popular herb for a different purpose: bolstering adaptations to weight training.
Does the Food Guide make my butt get fat?
By Francy Pillo-Blocka, RD
We’ve covered antioxidants and strength training before. This study is a bit different — it investigates whether vitamin C and vitamin E might impact adaptations to endurance exercise.
I <3 green tea
When it comes to curbing cardiovascular disease, it’s not all about reducing cholesterol. Green tea may help prevent oxidation of LDL, as is explored in this trial looking at green tea catechins both in vivo and in vitro.