Flexible vs. rigid dieting in resistance-trained individuals seeking to optimize their physiques: A randomized controlled trial

Abstract

Background The purpose of this study was to compare a flexible vs. rigid diet on weight loss and subsequent weight regain in resistance-trained (RT) participants in a randomized, parallel group design. Methods Twenty-three males and females (25.6 ± 6.1 yrs; 170 ± 8.1 cm; 75.4 ± 10.3 kg) completed the 20-week intervention (consisting of a 10-week diet phase and a 10-week post-diet phase). Participants were randomized to a flexible diet (FLEX) comprised of non-specific foods or a rigid diet (RIGID) comprised of specific foods. Participants adhered to an ~20%kcal reduction during the first 10-weeks of the intervention and were instructed to eat ad libitum for the final 10-weeks. Body composition and resting metabolic rate were assessed 5 times: (baseline, 5, 10 [end of diet phase], 16, and 20 weeks). Results During the 10-week diet phase, both groups significantly reduced bodyweight (FLEX: baseline = 76.1 ± 8.4kg, post-diet = 73.5 ± 8.8 kg, ▲2.6 kg; RIGID: baseline = 74.9 ± 12.2 kg, post-diet = 71.9 ± 11.7 kg, ▲3.0 kg, p < 0.001); fat mass (FLEX: baseline = 14.8 ± 5.7 kg, post-diet = 12.5 ± 5.0 kg, ▲2.3 kg; RIGID: baseline = 18.1 ± 6.2 kg, post-diet = 14.9 ± 6.5 kg, ▲3.2 kg p < 0.001) and body fat% (FLEX: baseline = 19.4 ± 8.5%, post-diet = 17.0 ± 7.1%, ▲2.4%; RIGID: baseline = 24.0 ± 6.2%, post-diet = 20.7 ± 7.1%, ▲3.3%; p < 0.001). There were no significant differences between the two groups for any variable during the diet phase. During the post-diet phase, a significant diet x time interaction (p < 0.001) was observed for FFM with the FLEX group gaining a greater amount of FFM (+1.7 kg) in comparison with the RIGID group (−0.7 kg). Conclusions A flexible or rigid diet strategy is equally effective for weight loss during a caloric restriction diet in free-living, RT individuals. While post-diet FFM gains were greater in the FLEX group, there were no significant differences in the amount of time spent in resistance and aerobic exercise modes nor were there any significant differences in protein and total caloric intakes between the two diet groups. In the absence of a clear physiological rationale for increases in FFM, in addition to the lack of a standardized diet during the post-diet phase, we refrain from attributing the increases in FFM in the FLEX group to their diet assignment during the diet phase of the investigation. We recommend future research investigate additional physiological and psychological effects of flexible diets and weight regain in lean individuals.

Weight regain, body composition, and metabolic responses to weight loss in weight cycling athletes: A systematic review and meta‐analyses

“…Then, seven studies were included in meta-analyses thanks to raw data sent by the authors, conducting 32 the total number of studies included in the meta-analyses. 2,[11][12][13]16,38,39,41,43,53,[78][79][80][81][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100]…”

“…articles do not report any significant changes in FFM at the end of the WG period, 50,53,56,85,87,88 and Kondo and collaborators 41 noted a significant increase of 1.2 kg (p < 0.05). Of the 9 articles that followed strength and conditioning athletes whose actual WL duration was known, 16,39,54,55,[80][81][82]96,97 4 were case studies. 16,[80][81][82] The subject-adjusted mean indicates a loss of 5.5 ± 4.1% of BW pre-WL in 1 82 to 7 months 80 of diet.…”

“…WG was estimated at 5.6 ± 3.5% of BW WL after 44.4 ± 57.9 days (range: 5-497 days) of recovery period. An increase in FM was highlighted and considered as significant in the two articles with apparent statistics (p < 0.05), 39,97 whereas a stable FFM was denoted. 39,54,55,81,82,97 Although these variations were observed for the RIGID diet group in the Conlin et al's study, the FLEX group had a significant increase in FFM, and no changes were observed for FM (kg).…”

Effects of Whey Protein Supplement on 4-Week Resistance Exercise-Induced Improvements in Muscle Mass and Isokinetic Muscular Function under Dietary Control

“…However, each person’s meal menu was diverse; therefore, it was difficult to match the exact calories in the food preparation process. Nevertheless, these unintentionally reduced calorie intakes could be considered to be within acceptable variability for a typical diet because even in previous studies with calorie restriction, the variation in calorie intake was approximately 6% to 10% [ 27 , 28 ]. Most weight loss programs reduce energy intake by 25–60% below the expected energy requirements, with the goal of losing an average of 5–8% of weight [ 29 , 30 , 31 ].…”

Intermittent Fasting and Fat Mass: What Is the Clinical Magnitude?

“…In addition, they provide micronutrients and antioxidants [47][48][49][50][51]. That said, incorporating small amounts of "unhealthy" foods can be accepted to maintain some of the patient's habits, but in moderation, as flexible dieting strategies have been deemed an important weight loss approach as a means of avoiding weight regain [52].…”