Anticipation of 24 h severe energy restriction increases energy intake and reduces physical activity energy expenditure in the prior 24 h, in healthy males

Intermittent fasting and bone health: a bone of contention?

Intermittent fasting (IF) is a promising strategy for weight loss and improving metabolic health, but its effects on bone health are less clear. This review aims to summarise and critically evaluate the preclinical and clinical evidence on IF regimens (the 5:2 diet, alternate-day fasting (ADF) and time-restricted eating (TRE)/time-restricted feeding and bone health outcomes. Animal studies have utilised IF alongside other dietary practices known to elicit detrimental effects on bone health and/or in models mimicking specific conditions; thus, findings from these studies are difficult to apply to humans. While limited in scope, observational studies suggest a link between some IF practices (e.g. breakfast omission) and compromised bone health, although lack of control for confounding factors makes these data difficult to interpret. Interventional studies suggest that TRE regimens practised up to 6 months do not adversely affect bone outcomes and may even slightly protect against bone loss during modest weight loss (< 5 % of baseline body weight). Most studies on ADF have shown no adverse effects on bone outcomes, while no studies on the ‘5–2’ diet have reported bone outcomes. Available interventional studies are limited by their short duration, small and diverse population samples, assessment of total body bone mass exclusively (by dual-energy X-ray absorptiometry) and inadequate control of factors that may affect bone outcomes, making the interpretation of existing data challenging. Further research is required to better characterise bone responses to various IF approaches using well-controlled protocols of sufficient duration, adequately powered to assess changes in bone outcomes and designed to include clinically relevant bone assessments.

Fasting Before Evening Exercise Reduces Net Energy Intake and Increases Fat Oxidation, but Impairs Performance in Healthy Males and Females

Acute morning fasted exercise may create a greater negative 24-hr energy balance than the same exercise performed after a meal, but research exploring fasted evening exercise is limited. This study assessed the effects of 7-hr fasting before evening exercise on energy intake, metabolism, and performance. Sixteen healthy males and females (n = 8 each) completed two randomized, counterbalanced trials. Participants consumed a standardized breakfast (08:30) and lunch (11:30). Two hours before exercise (16:30), participants consumed a meal (543 ± 86 kcal; FED) or remained fasted (FAST). Exercise involved 30-min cycling (∼60% VO2peak) and a 15-min performance test (∼85% VO2peak; 18:30). Ad libitum energy intake was assessed 15 min postexercise. Subjective appetite was measured throughout. Energy intake was 99 ± 162 kcal greater postexercise (p < .05), but 443 ± 128 kcal lower over the day (p < .001) in FAST. Appetite was elevated between the preexercise meal and ad libitum meal in FAST (p < .001), with no further differences (p ≥ .458). Fat oxidation was greater (+3.25 ± 1.99 g), and carbohydrate oxidation was lower (-9.16 ± 5.80 g) during exercise in FAST (p < .001). Exercise performance was 3.8% lower in FAST (153 ± 57 kJ vs. 159 ± 58 kJ, p < .05), with preexercise motivation, energy, readiness, and postexercise enjoyment also lower in FAST (p < .01). Fasted evening exercise reduced net energy intake and increased fat oxidation compared to exercise performed 2 hr after a meal. However, fasting also reduced voluntary performance, motivation, and exercise enjoyment. Future studies are needed to examine the long-term effects of this intervention as a weight management strategy.

Bariatric surgery-induced weight loss and associated genome-wide DNA-methylation alterations in obese individuals

BACKGROUND

Obesity is a multifactorial and chronic condition of growing universal concern. It has recently been reported that bariatric surgery is a more successful treatment for severe obesity than other noninvasive interventions, resulting in rapid significant weight loss and associated chronic disease remission. The identification of distinct epigenetic patterns in patients who are obese or have metabolic imbalances has suggested a potential role for epigenetic alterations in causal or mediating pathways in the development of obesity-related pathologies. Specific changes in the epigenome (DNA methylome), associated with metabolic disorders, can be detected in the blood. We investigated whether such epigenetic changes are reversible after weight loss using genome-wide DNA methylome analysis of blood samples from individuals with severe obesity (mean BMI ~ 45) undergoing bariatric surgery.

RESULTS

Our analysis revealed 41 significant (Bonferroni p < 0.05) and 1169 (false discovery rate p < 0.05) suggestive differentially methylated positions (DMPs) associated with weight loss due to bariatric surgery. Among the 41 significant DMPs, 5 CpGs were replicated in an independent cohort of BMI-discordant monozygotic twins (the heavier twin underwent diet-induced weight loss). The effect sizes of these 5 CpGs were consistent across discovery and replication sets (p < 0.05). We also identified 192 differentially methylated regions (DMRs) among which SMAD6 and PFKFB3 genes were the top hypermethylated and hypomethylated regions, respectively. Pathway enrichment analysis of the DMR-associated genes showed that functional pathways related to immune function and type 1 diabetes were significant. Weight loss due to bariatric surgery also significantly decelerated epigenetic age 12 months after the intervention (mean =  - 4.29; p = 0.02).

CONCLUSIONS

We identified weight loss-associated DNA-methylation alterations targeting immune and inflammatory gene pathways in blood samples from bariatric-surgery patients. The top hits were replicated in samples from an independent cohort of BMI-discordant monozygotic twins following a hypocaloric diet. Energy restriction and bariatric surgery thus share CpGs that may represent early indicators of response to the metabolic effects of weight loss. The analysis of bariatric surgery-associated DMRs suggests that epigenetic regulation of genes involved in endothelial and adipose tissue function is key in the pathophysiology of obesity.

Chrononutrition in Cardiometabolic Health

In recent years, a healthy balanced diet together with weight reduction has risen to the forefront of minimizing the impact of cardiovascular disease. There is evidence that metabolic processes present circadian rhythmicity. Moreover, the timing of food consumption exerts a powerful influence on circadian rhythms. In this context, the subject of chrononutrition, described as the alignment of timing of food intake to the rhythms imposed by the circadian clock, has attracted considerable interest for possible beneficial effects on cardiovascular health. Current human studies suggest that chrononutrition-based dietary interventions could reduce the risk for cardiovascular disease by improving weight control, hypertension, dyslipidemia, and diabetes. However, meta-analysis of randomized control trials in this topic present varying and somehow conflicting results. Even the traditional association of breakfast skipping with adverse cardiovascular outcomes is nowadays controversial. Therefore, long-term and fairly consistent studies on the effect of chrononutrition on cardiovascular outcomes are needed. The purpose of this review is to provide concise evidence of the most recent literature involving the effects of chrononutrition and the specific chrononutrition-based dietary interventions, in particular time-restricted eating, on body weight and other cardiovascular disease risk factors.

A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults

Intermittent fasting may impart metabolic benefits independent of energy balance by initiating fasting-mediated mechanisms. This randomized controlled trial examined 24-hour fasting with 150% energy intake on alternate days for 3 weeks in lean, healthy individuals (0:150; n = 12). Control groups involved a matched degree of energy restriction applied continuously without fasting (75% energy intake daily; 75:75; n = 12) or a matched pattern of fasting without net energy restriction (200% energy intake on alternate days; 0:200; n = 12). Primary outcomes were body composition, components of energy balance, and postprandial metabolism. Daily energy restriction (75:75) reduced body mass (-1.91 ± 0.99 kilograms) almost entirely due to fat loss (-1.75 ± 0.79 kilograms). Restricting energy intake via fasting (0:150) also decreased body mass (-1.60 ± 1.06 kilograms; P = 0.46 versus 75:75) but with attenuated reductions in body fat (-0.74 ± 1.32 kilograms; P = 0.01 versus 75:75), whereas fasting without energy restriction (0:200) did not significantly reduce either body mass (-0.52 ± 1.09 kilograms; P ≤ 0.04 versus 75:75 and 0:150) or fat mass (-0.12 ± 0.68 kilograms; P ≤ 0.05 versus 75:75 and 0:150). Postprandial indices of cardiometabolic health and gut hormones, along with the expression of key genes in subcutaneous adipose tissue, were not statistically different between groups (P > 0.05). Alternate-day fasting less effectively reduces body fat mass than a matched degree of daily energy restriction and without evidence of fasting-specific effects on metabolic regulation or cardiovascular health.

A Muscle-Centric Perspective on Intermittent Fasting: A Suboptimal Dietary Strategy for Supporting Muscle Protein Remodeling and Muscle Mass?

Muscle protein is constantly “turning over” through the breakdown of old/damaged proteins and the resynthesis of new functional proteins, the algebraic difference determining net muscle gain, maintenance, or loss. This turnover, which is sensitive to the nutritional environment, ultimately determines the mass, quality, and health of skeletal muscle over time. Intermittent fasting has become a topic of interest in the health community as an avenue to improve health and body composition primarily via caloric deficiency as well as enhanced lipolysis and fat oxidation secondary to attenuated daily insulin response. However, this approach belies the established anti-catabolic effect of insulin on skeletal muscle. More importantly, muscle protein synthesis, which is the primary regulated turnover variable in healthy humans, is stimulated by the consumption of dietary amino acids, a process that is saturated at a moderate protein intake. While limited research has explored the effect of intermittent fasting on muscle-related outcomes, we propose that infrequent meal feeding and periods of prolonged fasting characteristic of models of intermittent fasting may be counter-productive to optimizing muscle protein turnover and net muscle protein balance. The present commentary will discuss the regulation of muscle protein turnover across fasted and fed cycles and contrast it with studies exploring how dietary manipulation alters the partitioning of fat and lean body mass. It is our position that intermittent fasting likely represents a suboptimal dietary approach to remodel skeletal muscle, which could impact the ability to maintain or enhance muscle mass and quality, especially during periods of reduced energy availability.

An augmented food strategy leads to complete energy compensation during a 15-day military training expedition in the cold

Soldiers on military expeditions usually fail to compensate for the increase in energy expenditure, with potential deleterious consequences. We therefore analyzed the characteristics of energy compensation in 12 male soldiers, during a 15-day expedition in the cold, while alleviating some of the contextual limitations of food intake (~20-MJ daily bags of easy-to-use, highly palatable and familiar foods with multiple and long breaks allowed during the day). Body and fat mass losses were low and moderate, respectively (-1.13 ± 1.42% and -19.5 ± 15.6%, respectively, p < .021). Mean energy intake (EI) was high (~16.3 MJ) and increased at each third of the expedition (15.3 ± 2.1, 16.1 ± 2.1, and 17.6 ± 2.0 for D1-5, D6-10 and D11-15, respectively, p < .012). This resulted in reaching a neutral energy balance as soon as the D6 to 10 period and reaching normal energy availability during D11 to 15. Participants only increased their EI during the mid-day (10:00-14:00) period (p = .002) whereas hunger and thirst only increased in the morning, with higher scores during D11-15 than D1-5 (p < .009). Last, the reward value of sweet foods was also higher during D11-15 than during D1-5 (p = .026). The changes in body mass were positively associated with EI (r = 0.598, p = .040) and carbohydrate intake (r = 0.622, p = .031). This study indicates that complete energy compensation can be reached in challenging field conditions when food intake is facilitated, offering some guidelines to limit energy deficit during operational missions.

Negative energy balance during military training: The role of contextual limitations

During multiday training exercises, soldiers almost systematically face a moderate-to-large energy deficit, affecting their body mass and composition and potentially their physical and cognitive performance. Such energy deficits are explained by their inability to increase their energy intake during these highly demanding periods. With the exception of certain scenarios in which rations are voluntarily undersized to maximize the constraints, the energy content of the rations are often sufficient to maintain a neutral energy balance, suggesting that other limitations are responsible for such voluntary and/or spontaneous underconsumption. In this review, the overall aim was to present an overview of the impact of military training on energy balance, a context that stands out by its summation of specific limitations that interfere with energy intake. We first explore the impact of military training on the various components of energy balance (intake and expenditure) and body mass loss. Then, the role of the dimensioning of the rations (total energy content above or below energy expenditure) on energy deficits are addressed. Finally, the potential limitations inherent to military training (training characteristics, food characteristics, timing and context of eating, and the soldiers' attitude) are discussed to identify potential strategies to spontaneously increase energy intake and thus limit the energy deficit.

Realfooders Influencers on Instagram: From Followers to Consumers

(1) Background: Realfooders have positioned themselves in social networks such as Instagram by posting photographs of recipes, advises, habits and nutritional behaviours which are advertised as reliable nutritional patterns and by their self-promotion as highly trained people in the field of nutrition which sometimes jeopardises the health of digital citizenry. (2) Methods: In this article, we develop a quantitative study for analysing the influence of selected Realfooders on 2,866,980 followers on Instagram, taking into account channel variables (gender, location, interests and motivations), followers’ variables (engagement, interaction and consumption) and some variables related to the message of 54 posts about breakfast. (3) Results: Selected Realfooders concentrate their followers in Spain, mostly women between 18 and 24 and between 35 and 44 years old who link their interests on food to the cult of the body and recreational areas. On the other hand, the content generated by Realfooders has been increasing its impact using advertising and marketing techniques for awaking consumer’s interest. (4) Conclusions: Educational and social agents are facing the challenge of low health literacy in young population. Therefore, it is necessary to design and implement strategies for developing critical thinking that allow them to assess the content generated by Realfooders and identify which recommendations can be harmful or beneficial to their health.

An exploratory investigation of the impact of 'fast' and 'feed' days during intermittent energy restriction on free-living energy balance behaviours and subjective states in women with overweight/obesity

BACKGROUND/OBJECTIVES

This controlled-feeding randomised controlled trial examined free-living appetite and physical activity (PA) on 'fast' and 'feed' days during intermittent energy restriction (IER), compared to continuous energy restriction (CER).

SUBJECTS/METHODS

Forty-six women with overweight/obesity (age = 35 ± 10 years, BMI = 29.1 ± 2.3 kg/m²) were randomised to IER (n = 24; alternate fast days at 25% energy requirements and ad libitum feed days) or CER (n = 22; 75% energy requirements daily) to ≥5% weight loss (WL) or up to 12 weeks. Self-reported energy intake (EI; online food record), objectively measured PA (SenseWear Armband) and retrospective daily hunger and food cravings were measured over 7 days at baseline, week 2 and final week. Intent-to-treat analyses were performed using linear mixed models.

RESULTS

Final WL (M_Δ = 4.7 [95% confidence interval 4.2, 5.2] kg, 5.9%) did not differ between IER and CER (interaction P = 0.307). During IER, feed-day EI did not differ from baseline and was lower in the final week compared to week 2 (M_Δ = 295 [81, 509] kcal, P = 0.004). Daily hunger was greater on fast compared to feed days (M_Δ = 15 [10, 21] mm, P < 0.001), but food cravings did not differ. Light PA was lower on fast relative to feed days (M_Δ = 18 [2, 34] min/day, P = 0.024), with no other differences in PA. Compared to CER, IER increased hunger and led to smaller improvements in craving control (both interactions P ≤ 0.034).

CONCLUSIONS

IER fast days were associated with increased free-living hunger and lower light PA compared to feed days, but had no impact on food cravings or self-reported ad libitum daily EI. IER may be less favourable than CER for the free-living day-to-day control of hunger and food cravings.