A 3-day high-fat/low-carbohydrate diet does not alter exercise-induced growth hormone response in healthy males

Highlights

• It could not be confirmed that a 3-day high-fat/low-carbohydrate diet altered significantly exercise-induced growth hormone response despite of increased FFA level.

• Exercise-induced lipolytic and fat-oxidative responses were enhanced by consumption of high-fat/low-carbohydrate diet for three days.

• Intramyocellular lipid contents did not change after short-term consuming high-fat/low-carbohydrate diet.

Abstract

Objective

The purpose of the present study was to examine the effects of 3 days isoenergetic high-fat/low-carbohydrate diet (HF-LC) relative to low-fat/high-carbohydrate diet (LF-HC) on the exercise-induced growth hormone (GH) response in healthy male subjects.

Design

Ten healthy young males participated in this study. Each subject consumed the HF-LC (18 ± 1% protein, 61 ± 2% fat, 21 ± 1% carbohydrate, 2720 kcal per day) for 3 consecutive days after consuming the LF-HC (18 ± 1% protein, 20 ± 1% fat, 62 ± 1% carbohydrate, 2755 kcal per day) for 3 consecutive days. After each dietary intervention period, the hormonal and metabolic responses to an acute exercise (30 min of continuous pedaling at 60% of $\dot{\mathrm{V}}$O_2max) were compared. The intramyocellular lipid (IMCL) contents in the vastus lateralis, soleus, and tibialis anterior were evaluated by proton magnetic resonance spectroscopy.

Results

Serum GH concentrations increased significantly during the exercise after both the HF-LC and LF-HC periods (P < 0.05). However, the exercise-induced GH response was not significantly different between the two periods. Fat utilization and lipolytic responses during the exercise were enhanced significantly after the HF-LC period compared with the LF-HC period. IMCL content did not differ significantly in any portion of muscle after the dietary interventions.

Conclusions

We could not show that short-term HF-LC consumption changed significantly exercise-induced GH response or IMCL content in healthy young males.

Introduction

Exercise is well known to be a powerful physiological stimulus for growth hormone (GH) secretion [1], [2], [3], [4], [5] and a single bout of exercise can evoke dramatic increase in GH concentration [6]. Additionally, increased GH concentration enhances acute lipolysis [7], [8], [9], and 24-h energy expenditure and fat oxidation in healthy adults [10]. Therefore, an elevated GH concentration with exercise is thought to play a role in preventing obesity.

Diet composition prior to exercise affects exercise-induced GH response. Consuming a high-fat meal 45 min before exercise markedly attenuates exercise-induced GH response [11], [12] due to increasing somatostatin concentration, which inhibits GH secretion [11], [13]. Meanwhile the influence of short-term (several days) fat loading on exercise-induced GH response has not been fully investigated. To our knowledge, only one study [14] investigated the effects of short-term high-fat intake on exercise-induced GH response. The above study [14] reported that short-term (1.5 days) consumption of high-carbohydrate diet plus fat supplementation did not alter exercise-induced GH response compared with high-carbohydrate diet alone. The absence of change in exercise-induced GH response was likely due to the lack of change in free fatty acid (FFA) concentration, because systemic FFA elevation suppressed GH secretion [15], [16], [17], [18]. However, the influence of several days of high-fat/low-carbohydrate diet consumption on exercise-induced GH response is still questionable, because the previous study [14] utilized high-carbohydrate diet (high-fat/high-carbohydrate diet), which results in impaired high-fat induced FFA elevation by stimulating insulin secretion. Currently, we need to confirm that whether exercise-induced GH response is maintained when the subjects consume high-fat/low-carbohydrate diet.

GH secretion is inversely associated with whole body or visceral fat mass [19]. In fact, obese people with marked abdominal fat have impaired spontaneous [20], [21] and exercise-induced GH responses [5], [22], [23] compared with normal-weight people. Interestingly, some studies have suggested that fat accumulated in the non-adipose tissue (e.g., muscle and liver) depot also attenuates GH secretion. In previous studies, peak GH concentration following GH releasing hormone and arginine administration has been shown to be inversely correlated with the intramyocellular lipid (IMCL) content [24], [25]. Furthermore, the accumulation of IMCL is caused by increasing dietary fat. Short-term (2–7 days) high-fat/low-carbohydrate diet (HF-LC) increases IMCL by 36–76% compared with isoenergetic low-fat/high-carbohydrate diet (LF-HC) [26], [27], [28], [29]. Therefore, we hypothesized that exercise-induced GH response would be impaired by several days of HF-LC consumption in young healthy adults. Thus, the present study was designed to compare changes in exercise-induced GH response and IMCL content between 3 successive days of HF-LC and LF-HC in healthy young males. This experimental approach mimics realistic situation, as a temporal increase in fat intake for several days (e.g., increased fat consumption during the weekend) occurs frequently in modern life.