In a recent review published in Nutrition Research Reviews, researchers compared the effects of energy-restricted (ER) dietary patterns with nuts or without on body composition, weight, and glycemic management.
Background
Nutritionists advise energy-restricted diets for weight loss, better body composition, and glycemic management. However, maintaining a high diet quality might be difficult owing to the need to satisfy vital dietary requirements.
Nuts, a nutrient-dense food, can help meet these diet requirements. However, nuts are high in energy, prompting concerns regarding their use in weight-loss programs.
The data on the impact of nut intake on glycemic indices is inconsistent, whether in healthy individuals or those with metabolic syndrome, dyslipidemia, or prediabetes. It is unclear if including nuts in ER diets might enhance glycemic control even more.
About the review
In the present scoping review, researchers investigated whether incorporating nuts into a calorie-restricted diet affects anthropometric measurements and glycemic management in overweight or obese individuals.
The researchers examined the Medline, Scopus, and Embase databases for randomized controlled trials (RCTs) in individuals to evaluate the impact of energy-restricted diets with or without nuts on body mass, body composition, and glycemic management. The RCTs comprised overweight [body mass index (BMI) 25 to 29.90 kg m-2] or obese (BMI ≥30 kg m-2) individuals with comorbidity presence or absence who had engaged in weight reduction dietary treatments.
The researchers undertook the literature search on April 12, 2021, and again on January 25, 2022. An academic librarian at South Australia University analyzed keywords and topic headings. Two investigators independently reviewed titles, abstracts, and entire texts, with a third investigator resolving discrepancies.
The researchers evaluated studies if their intervention included nut-enriched calorie-restricted diets and measured blood glucose using the following methods: venous glucose, interstitial fluid glucose, or fasting blood glucose, sampled via venous blood draws, finger pricking, flash glucose monitors, or continuous-type glucose monitoring (CGM). Eligible studies evaluated both fasting glucose and body mass. Every calorie-restricted diet included one or more varieties of tree nuts or peanuts in whole, paste, or chopped form.
The researchers excluded studies in which ER diets included nut oils or nuts in addition to another meal or as a component of a diet pattern that made identifying the sole effect of nut ingestion impossible. They excluded observational and non-interventional studies, opinion articles, conference papers, and animal cell culture experiments. They also excluded records published in non-peer-reviewed journals in non-English languages.
Results and discussion
The initial search yielded 859 publications. After removing 166 duplicates, the researchers performed title-abstract screening for 693 studies and reviewed the entire text of 29 publications, with seven investigations described in eight papers meeting the inclusion criteria. The study’s publication dates spanned from 2003 to 2022. Study locations were primarily North America, Brazil, and Iran. All trials involved 676 individuals aged 18 to 79 years.
Energy limitation was accomplished by setting a specific energy target or limiting consumption by 1,000 to 4,200 kJ from daily energy needs. Interventions lasted 28 days to 52 weeks and included 42 to 84 g/day of peanuts (with and without skin), almonds, walnuts, or pistachios. Although energy restriction can cause considerable weight reduction, adding nuts to ER diets led to increased weight loss in only four of seven trials.
The researchers found that a nut-enriched ER diet lowered weight from -22.6 to -19.5 kg (percentage loss: -3.0% to -18%) or -0.1 to -0.2 kg per week. The increased benefit of the nut-enriched ER diets varied from -1.4 to 0.4 kg. The time of supplementation, anthropometric measurements, and kind of nuts ingested were among the most significant variations between trials.
Nuts include essential fatty acids (EFAs), which can enhance glycemic management by lowering pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and insulin resistance. Their low carbohydrate and high unsaturated fat, fiber, B vitamins, magnesium, and protein composition increase fat oxidation, slow stomach emptying, and decrease postprandial glucose levels. Nuts also increase satiety, retain muscle mass, and reduce the resting energy expenditure associated with weight loss. Their complex plant cell wall matrices inhibit enzymatic breakdown.
The research found limited evidence to support the advantages of nuts for body composition or glycemic management. While advantages in weight reduction and glycemia were variable when adding nuts to energy-restricted diets, there were no adverse effects. The level of calorie restriction varied among studies, as did the kind and quantity of nuts used. All trials found that an energy-restricted diet improved body mass with variable effects on glucose and insulin.
Future research should evaluate the duration and macronutrient content of nut consumption and investigate the impact of different nut types and amounts, along with varying energy levels, on weight, body composition, and glycemic control among diverse populations with varied medical and ethnic backgrounds.