Effects of Peanuts as a Nighttime Snack Compared to a Lower-Fat Higher-Carbohydrate Control on Glycemic Control, Cardiovascular Disease Risk Factors, and the Gut Microbiota in Adults with Elevated Fasting Glucose
Open Access
- Author:
- Sapp, Philip
- Graduate Program:
- Nutritional Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 19, 2021
- Committee Members:
- Vishal Singh, Major Field Member
Penny Kris-Etherton, Chair & Dissertation Advisor
Gregory Shearer, Major Field Member
Michael Russell, Outside Unit & Field Member
Kristina Petersen, Special Member
Laura Murray-Kolb, Program Head/Chair - Keywords:
- fasting glucose
peanut
cardiometabolic health
supplemental feeding study
diet quality
elevated fasting glucose - Abstract:
- The aim of this dissertation was to investigate the cardiometabolic effects of consuming peanuts as a nighttime snack, compared to a lower-fat higher-carbohydrate (LFHC) snack, in adults with elevated fasting glucose. In a randomized controlled, crossover, supplemental feeding study design, participants consumed the nighttime snacks for 6 weeks with ≥ 4-week compliance break between conditions. The conditions were 28.4 g dry roasted, unsalted, peanuts (164 kcal; 11% E carbohydrate, 17% E protein, and 73% E fat) and 6 whole grain crackers with one slice of low-fat American cheese (164 kcal; 53% E carbohydrate, 17% E protein, and 33% E fat). Participants were instructed to consume the study foods after dinner, before bedtime, and consume no other food or drinks containing calories after their snack. Additionally, participants were instructed to avoid consuming any other peanuts, or tree nuts, for the duration of the study. The primary outcome was fasting plasma glucose and secondary outcomes were weight, insulin, fructosamine, lipids/lipoproteins, brachial blood pressure (BP), central BP, measures of arterial stiffness [pulse wave velocity (PWV)], diet quality, and the gut microbiota with each of these outcomes being assessed at baseline and endpoint for both conditions. Diet quality, measured by the Healthy Eating Index-2015 (HEI-2015), was assessed using the Automated Self-Administered 24-recall system (ASA24). Fecal samples from all participants (n=50) were analyzed using 16S rRNA sequencing to assess gut microbiota composition and diversity while a subset of samples from responders (n=24) to the peanut condition (greatest reduction in fasting glucose) were analyzed using metatranscriptomics to assess bacterial gene expression. Fifty adults with elevated fasting glucose (52% male; age: 42 ± 15 years; BMI: 28.3 ± 5.6 kg/m2; fasting plasma glucose: 100 ± 8 mg/dL) completed the study. There were no significant between-condition mean differences for fasting plasma glucose (Peanut vs. LFHC -0.6 mg/dL; 95% CI: -2.7, 1.6; P = 0.67). There were no between-condition mean differences for weight, fructosamine, lipid/lipoproteins, brachial BP, central BP, or PWV. Total energy intake was not different between conditions, but percent of energy from polyunsaturated and monounsaturated fatty acids was higher following the Peanut condition compared to the LFHC condition (1.9%; 95% CI: 0.0, 3.4; P = 0.01 and 1.7%; 95% CI: 0.0, 3.4; P = 0.04). No between-condition mean difference for total HEI-2015 score was observed (Peanut vs. LFHC 3.6 points; 95% CI: -1.9, 9.0; P = 0.19). Examination of the HEI-2015 components showed that the added sugar (0.8 points; 95% CI: 0.0, 1.5; P = 0.04) and seafood/plant protein (2.0 points; 95% CI: 1.0, 2.9; P < 0.01) components were higher following the Peanut condition vs. the LFHC snack. The whole grain (-2.6 points; 95% CI: -3.8, -1.4; P < 0.01) component was lower with the Peanut snack vs. LFHC. No other HEI-2015 components were different between the conditions. There were no between-condition differences in microbiota α- diversity or β-diversity. Following the Peanut condition, Roseburia [linear discriminant analysis score (LDA) = 3.1; P = 0.035)] and Ruminococcaceae (LDA = 2.8; P = 0.037) were significantly enriched compared to the LFHC snack. In the meta-transcriptomics exploratory analyses, a significant increase in expression of the K03518 (aerobic carbon-monoxide dehydrogenase small subunit) gene (LDA = 2.0; P = 0.039) was observed following peanut intake compared to baseline. Taxonomic contributor analyses showed Roseburia Instinalis L1 contributed to the increase in K03518 gene expression (1.5% contribution in endpoint samples vs. no detectable contribution in baseline samples). In adults with elevated fasting glucose, consuming 28 g of dry roasted, unsalted, peanuts as a nighttime snack did not alter fasting plasma glucose compared to a LFHC nighttime snack. Consumption of peanuts compared to the LFHC snack did not increase weight or total energy intake but was associated with improvements in the fatty acid profile of the diet. Peanuts improved seafood/plant protein and added sugar diet quality components but reduced the whole grain component compared to a LFHC control. Several SCFAs producing bacteria were enriched following peanut intake and expression of a gene associated with fiber degradation and SCFAs production was increased. Consuming peanuts as a nighttime snack compared to a LFHC nighttime snack does not have adverse effects on fasting plasma glucose in adults with elevated fasting glucose and improves several aspects of dietary intake and quality with beneficial impacts on gut microbiota composition and functionality.