RESUMO

Background: Observational evidence suggests higher nut consumption is associated with better glycemic control; however, it is unclear if this association is causal. Objectives: We aimed to conduct a systematic review and meta-analysis of randomized controlled trials to examine the effect of tree nuts and peanuts on markers of glycemic control in adults. Methods: A systematic review and meta-analysis of randomized controlled trials was conducted. A total of 1063 potentially eligible articles were screened in duplicate. From these articles, 40 were eligible for inclusion and data from these articles were extracted in duplicate. The weighted mean difference (WMD) between the nut intervention and control arms was determined for fasting glucose, fasting insulin, glycated hemoglobin (HbA1c), and homeostasis model assessment of insulin resistance (HOMA-IR) using the DerSimonian and Laird random-effects method. For outcomes where a limited number of studies were published, a qualitative synthesis was presented. Results: A total of 40 randomized controlled trials including 2832 unique participants, with a median duration of 3 mo (range: 1-12 mo), were included. Overall consumption of tree nuts or peanuts had a favorable effect on HOMA-IR (WMD: -0.23; 95% CI: -0.40, -0.06; I2 = 51.7%) and fasting insulin (WMD: -0.40 µIU/mL; 95% CI: -0.73, -0.07 µIU/mL; I2 = 49.4%). There was no significant effect of nut consumption on fasting blood glucose (WMD: -0.52 mg/dL; 95% CI: -1.43, 0.38 mg/dL; I2 = 53.4%) or HbA1c (WMD: 0.02%; 95% CI: -0.01%, 0.04%; I2 = 51.0%). Conclusions: Consumption of peanuts or tree nuts significantly decreased HOMA-IR and fasting insulin; there was no effect of nut consumption on HbA1c or fasting glucose. The results suggest that nut consumption may improve insulin sensitivity. In the future, well-designed clinical trials are required to elucidate the mechanisms that account for these observed effects.

Assuntos

RESUMO

There is concern that tree nuts may cause weight gain due to their energy density, yet evidence shows that tree nuts do not adversely affect weight status. Epidemiologic and experimental studies have shown a reduced risk of chronic diseases with tree nut consumption without an increased risk of weight gain. In fact, tree nuts may protect against weight gain and benefit weight-loss interventions. However, the relation between tree nut consumption and adiposity is not well understood at the mechanistic level. This review summarizes the proposed underlying mechanisms that might account for this relation. Evidence suggests that tree nuts may affect adiposity through appetite control, displacement of unfavorable nutrients, increased diet-induced thermogenesis, availability of metabolizable energy, antiobesity action of bioactive compounds, and improved functionality of the gut microbiome. The gut microbiome is a common factor among these mechanisms and may mediate, in part, the relation between tree nut consumption and reduced adiposity. Further research is needed to understand the impact of tree nuts on the gut microbiome and how the gut microbial environment affects the nutrient absorption and metabolism of tree nuts. The evidence to date suggests that tree nut consumption favorably affects body composition through different mechanisms that involve the gut microbiome. A better understanding of these mechanisms will contribute to the evolving science base that addresses the causes and treatments for overweight and obesity.

RESUMO

Clusters of bacterial species within the gut microenvironment, or gut enterotype, have been correlated with cardiometabolic disease risk. The metabolic products and metabolites that bacteria produce, such as short-chain fatty acids, secondary bile acids, and trimethylamine, may also affect the microbial community and disease risk. Diet has a direct impact on the gut microenvironment by providing substrates to and promoting the colonization of resident bacteria. To date, few dietary patterns have been evaluated for their effect on the gut microbiome, but the Mediterranean diet and Vegetarian diets have shown favorable effects for both the gut microbiome and cardiometabolic disease risk. This review examines the gut microbiome as a mediator between these dietary patterns and cardiometabolic disease risk.

Assuntos

RESUMO

Diets rich in plant foods are increasingly recommended to lower the risk of cardiometabolic diseases because of strong evidence that fruit, vegetables, legumes, whole grains, nuts, and seeds are protective. Although some animal products, such as unprocessed lean red meat, poultry, eggs, and dairy products, are recommended in dietary patterns to prevent cardiometabolic diseases, many health professionals advocate for exclusively plant-based dietary patterns. The aim of this article was to review recent evidence on the relative contributions of plant-based foods and animal products to a healthy dietary pattern. Secondary aims were to discuss current consumption patterns and adherence to dietary recommendations. Epidemiologic evidence suggests that a higher intake of plant-based foods is associated with a lower risk of cardiometabolic disease, whereas a higher meat intake increases the risk of cardiometabolic disease and the replacement of small quantities of animal protein with plant protein is associated with lower risk. Randomized controlled studies show that nutrient-dense diets containing animal protein, including some unprocessed lean meats, improve cardiovascular disease risk factors. Therefore, it is likely that the consumption of animal products, at recommended amounts, in the context of a dietary pattern that meets recommendations for fruit, vegetables, whole grains, nuts, seeds, and legumes, and does not exceed recommendations for added sugar, sodium, and saturated fat, may not increase cardiometabolic risk. Currently, adherence to these recommendations is suboptimal. Therefore, rather than debating the merits of healthy dietary patterns that are exclusively plant-based or that include animal sources in recommended amounts, the focus should be on improving overall eating patterns to align with dietary guidelines. Registered Dietitian/Nutritionists (RDNs) have the requisite nutrition expertise to facilitate change at the individual and population levels to promote adherence to healthy dietary patterns. Importantly, advocacy activities are urgently needed to create a healthier food environment, and all health professionals, including RDNs, must play a role.