Effects of Protein Timing and Resistance Exercise on Fat Metabolism

Nighttime eating, and specifically eating after dinner, has attracted significant attention in recent years, particularly for the onslaught of media claiming the negative implications on body weight and overall health. Some studies have indeed indicated that chronically eating high-energy, mixed-meals rich in carbohydrates (CHO) and fats at night contributes to weight gain and abdominal obesity. However, research to support these negative claims is scant. Conversely, the practice of nighttime eating of small protein (PRO) snacks has been widely utilized anecdotally in populations such as bodybuilders in an attempt to avoid catabolism of muscle mass during the sleeping hours.

It has been shown that nighttime consumption of small portions (<200 kcals) of PRO elicits beneficial effects on metabolism such as increased next-morning resting metabolic rate (RMR). Likewise, the combination of nighttime PRO consumption and RT improves factors that contribute to fat loss such as elevated muscle mass due to an increase in muscle protein synthesis and energy expenditure. Further, there is emerging research suggesting the benefits of nighttime PRO consumption on fat metabolism (specifically the subcutaneous abdominal adipose tissue [SCAAT]). The SCAAT is of particular interest in metabolism research, as the upper body subcutaneous tissue (i.e. SCAAT) supplies most of the circulating free fatty acids (FFA) during the overnight hours in lean individuals. Therefore, if one can optimize the timing of dietary PRO during a window at which SCAAT is elevated (nighttime), theoretically, mobilization and oxidation of fats could be optimized.

Research regarding nighttime eating, specifically regarding fat metabolism, is in its infancy, and thus, many gaps in the literature require elucidation. First, and certainly most importantly, the limited research studies examining the effects of nighttime PRO consumption have not methodologically matched for timing of PRO intake. Therefore, it is unclear whether any reported benefits of the published nighttime PRO studies were a consequence of the addition of PRO calories or specifically due to the consumption of PRO at night. Thus, in order to make optimal comparisons and conclusions, it is imperative to study the metabolic effects of dietary PRO consumed at night versus other times of day.

Therefore, the purpose of this project is to: 1) determine the effects of RT on post-exercise lipolytic rate in resistance-trained women; and 2) determine the effects of timing of acute protein PRO ingestion (nighttime PRO consumption [NP] and daytime PRO consumption [DP] trials) after a RT bout on SCAAT lipolytic rate, metabolic rate, and serum hormones (glucose, insulin, growth hormone, adiponectin, glycerol) throughout the day, overnight and into the next morning.

Inclusion criteria

• Healthy
• Resistance-trained (able to squat 1.0 times their body weight, and bench press 0.75 times body weight, adapted from ACSM Guidelines and piloted in our laboratory)
• Normal weight (BMI = 18.5-25 kg/m2; body fat <33%)
• Normally menstruating (on or off oral contraceptives)
• Females.

Exclusion criteria

• Uncontrolled thyroid dysfunction (not on medication)
• Musculoskeletal disorders
• Currently smoke
• Have milk allergies
• Currently take medications or supplements known to affect substrate metabolism.