Abstract
There is an increasing trend in the consumption of poor-quality diets worldwide, contributing to the increase of non-communicable diseases. Diet directly influences physiological composition and subsequently physical health. Studies have shown that dietary macronutrient and energy content can influence the proportion of intramuscular fat (IMF), which mediates various metabolic and endocrine dysfunction. The purpose of this systematic review was to identify evidence in the literature assessing the association between different dietary interventions on the proportion of IMF in humans. Three medical databases were investigated (Medline, EMBASE, and Cochrane) to identify studies assessing changes in IMF after dietary interventions. The primary outcome measure was the change in IMF proportions after a dietary intervention. The effects of high-fat, high-carbohydrate, low-calorie, and starvation diets were assessed qualitatively. A meta-analysis assessing the effect of high-fat diets was conducted. Follow-up sensitivity and subgroup analyses were also conducted. One thousand eight hundred and sixty-six articles were identified for review. Of these articles, 13 were eligible for inclusion after a full screening. High-fat diets increased IMF proportions, standardized mean difference = 1.24 (95% confidence interval, 0.43-2.05) and a significant overall effect size (P = 0.003). Diets with an increased proportion of carbohydrates decreased IMF proportions; however, increasing caloric intake with carbohydrates increased IMF. Starvation diets increased IMF stores, and hypocaloric diets did not result in any IMF proportion changes. This systematic review suggests that high-fat diets and diets with caloric intake increased above the amount required to maintain BMI with carbohydrates, and short-term starvation diets are associated with increases in IMF content. Further studies are needed to assess the effects of macronutrient combinations on IMF and the influence of diet-induced IMF alterations on health outcomes. In addition, IMF poses a possibly effective clinical marker of health.
Highlights
The prevalence of poor-quality diets has increased worldwide in the past two decades, presenting as a main contributor to the increasing rates of chronic illness and mortality (1, 2)
Our systematic review suggests that high-fat diets, excessive caloric intake in the form of carbohydrates, and short-term starvation diets are associated with increases in Intramuscular fat (IMF) content
A robust association between high-fat diets and IMF content is presented in this study
Summary
The prevalence of poor-quality diets has increased worldwide in the past two decades, presenting as a main contributor to the increasing rates of chronic illness and mortality (1, 2). Intramuscular fat (IMF) proportions are principal mediators of various metabolic and endocrine functions that lead to these diseases (7, 8). Studies have shown that dietary macronutrient distribution and energy content can influence the proportion of IMF (9–11). Buettner et al (14) and van den Broek et al (15) report increases in the proportion of IMF with high-fat diets in rodents. High-fat diets are associated with increases in IMF levels in humans (16). The effects of high-carbohydrate and low-calorie/starvation diets on IMF present conflicting results in the literature. Very low-calorie or starvation diet interventions result in conflicting IMF content changes. There are reports of significantly higher proportions of IMF following starvation or low-calorie interventions (19, 20). Studies have shown that dietary macronutrient and energy content can influence the proportion of intramuscular fat (IMF), which mediates various metabolic and endocrine dysfunction. The purpose of this systematic review was to identify evidence in the literature assessing the association between different dietary interventions on the proportion of IMF in humans
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