Emerging insights in weight management and prevention: implications for practice and research

Recent advances in foundational research on energy balance and weight loss shed new light on earlier findings. Emerging evidence and insights around mental illness and client-centred, weight-inclusive approaches have implications for practitioners. This paper provides an overview of opinions from invited experts who presented at the Canadian Nutrition Society Thematic Conference in January 2019. Novelty: Weight loss involves an interplay of multiple factors, not diet alone. There is no "best diet" or treatment approach for weight loss. Future research should involve minimizing weight loss countermeasures and new health system-based approaches aimed at improving health.

Dietary restriction and/or exercise training impairs spermatogenesis in normal rats

Dietary restriction and/or exercise has been shown to have multiple benefits for health. However, its effects on reproductive health and the mechanisms by which it regulates reproductive function remain unclear. Here, to evaluate its effects on spermatogenesis and sperm function, rats were divided into 4 groups: ad libitum-fed sedentary control, dietary restriction (DR), exercise training (ET), and dietary restriction plus exercise training (DR+ET) groups. Results indicated that body weight, epididymal fat pad weight, and sperm counts were significantly reduced in the DR, ET, and DR+ET groups. Moreover, sperm motility and capacitation-associated protein tyrosine phosphorylation were suppressed in the DR and DR+ET groups, but not the ET group. Microarray analysis revealed that the number of downregulated genes was higher than that of upregulated genes in the DR and/or ET groups. About half of the downregulated genes are common after exercise training and/or diet restriction. Gene ontology analysis showed that downregulated genes in the DR, ET, and DR+ET groups affected spermatogenesis through overlapping pathways, including glucocorticoid, corticosteroid, extracellular structure organization, and estradiol responses. Our findings suggest that diet restriction and/or exercise training may present potential risks to male reproductive dysfunction by disrupting normal gene expression patterns in the testis. Novelty: Dietary restriction and/or exercise can lead to the damage of spermatogenesis as well as sperm maturation. Sperm functional changes are more sensitive to dietary restriction than exercise training. Dietary restriction and exercise impair spermatogenesis through overlapping biological pathways in the testis.

Dietary restriction slightly affects glucose homeostasis and delays plasma cholesterol removal in rabbits with dietary lipid lowering

Dietary restriction (DR) has been reported to have beneficial effects on atherosclerotic progression as well as lipid and glucose metabolism, but little is known about whether these effects can be enhanced or weakened by dietary lipid lowering. Here, after 12 weeks of high-cholesterol diet feeding, hypercholesterolemic rabbits were fed with either a standard chow diet ad libitum (AL) or a standard chow diet with DR for 16 weeks of dietary lipid lowering. We found that the DR group exhibited a loss of body weight, smaller internal organs, and reduced fat mass, while the AL group accumulated more subcutaneous fat than the baseline group. DR treatment slightly worsened glucose tolerance but enhanced insulin sensitivity, and a slight effect of DR on insulin secretion was also observed. After dietary cholesterol withdrawal, rabbits showed persistent lowering of total cholesterol and triglycerides in plasma. However, the DR group had significantly higher plasma total cholesterol than the AL group at most time points during weeks 7 to 16 of lipid lowering. Although both the AL and DR groups developed more severe atherosclerosis than the baseline group, DR did not improve atherosclerotic progression or the accumulation of macrophages and smooth muscle cells. We conclude that DR affected glucose and lipid metabolism but did not ameliorate atherosclerosis in rabbits when associated with lipid lowering by dietary cholesterol withdrawal.

Dietary restriction in moderately obese rats improves body size and glucose handling without the renal and hepatic alterations observed with a high-protein diet

Obesity is increasing worldwide, and high-protein (HP) diets are widely used for weight loss. However, the overall safety of HP diets is not well established in obese individuals, who make up a significant proportion of the population. To evaluate the health effects of an HP diet in obesity, obesity-prone (OP) Sprague-Dawley rats were given high-fat diets for 12 weeks to induce obesity. Following this, for 8 more weeks, these rats were given either a normal-protein (NP) (15% of energy) or an HP (35% of energy) diet ad libitum, or the NP diet at a restricted level to achieve body weights similar to those of the HP group (pair-weighted (PW) group). Obesity-resistant (OR) control rats were also given the NP diet throughout the feeding period. The HP-OP group had higher food intake but lower body weight, improved glucose handling, and lowered serum haptoglobin compared with the NP-OP group. These benefits were also observed in PW-OP rats. In addition, PW-OP rats had less fat accumulation when compared with NP-OP rats, and an improved Lee index, lower liver size, and lower serum alanine aminotransferase when compared with HP-OP rats. On the other hand, kidney size, proteinuria, and serum homocysteine were increased in HP-OP rats compared with NP-OP rats, whereas PW-OP rats did not experience these effects. These results indicate that in obese rats, more benefits are obtained via dietary restriction with an NP diet and without some of the potentially detrimental effects of an HP diet.