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Whole grain diet reduces body weight, ineffective in gut microbiome
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Compared with diets higher in refined grains, whole grain diets did not alter insulin sensitivity or the gut microbiome, according to a recently published study. However, results of the study revealed that diets higher in whole grains reduced body weight and systemic low-grade inflammation.
“Most people will benefit from choosing whole grains instead of refined grains. Generally speaking, wholegrain consumption gives prolonged satiety which over time may result in a lower body weight,” Henrik Munch Roager, from the National Food Institute, Technical University of Denmark, told Healio.com/Hepatology. “Furthermore, consumption of whole grains lowers the concentrations of inflammatory markers in the circulation, possible due to the beneficial compounds present in whole grains.”
To address the hypothesis that replacement of refined grains with whole grains improves insulin sensitivity and alters gut microbiome, the researchers designed a randomized cross-over trial of dietary intervention among patients with risk for metabolic syndrome.
“Whole grains are rich in phenolic phytochemicals and dietary fibers that are metabolized by the gut microbiota into short-chain fatty acids (SCFA), which have been linked to secretion of gut hormones, glucose and lipid metabolism, immune homeostasis and gut permeability,” Roager and colleagues wrote. “Only a limited number of human interventions have related whole grain-induced improvements on host metabolism with fecal microbiota composition, and so far the results have been inconclusive.”
According to Roager and colleagues, previous evidence linked whole grain consumption with decreased risk for type 2 diabetes and cardiovascular diseases.
The study included 50 adults aged 20 years to 65 years with BMI between 25 kg/m2 and 35 kg/m2 and waist circumference of 94 cm or higher for men (n = 18) or 80 cm or higher for women (n = 32). Patients also had non-diabetic dysglycemia, dyslipidemia, cholesterol levels of 1.03 mmol/L or lower for men or 1.29 mmol/L or lower for women, or hypertension.
For two 8-week dietary intervention periods, separated by a washout period of at least 6 weeks, patients consumed 75 or more grams per day of whole grains and less than 10 grams per day of refined grain intervention during either the first or second week and otherwise followed a refined grain diet the other week.
Investigators reported that patients complied well with both diets: whole grain consumption and fasting plasma alkylresorcinol concentrations were significantly higher during the grain-based dietary period (P < .0001).
Energy intake from the provided food products was 14% higher during the refined grain diet period compared with the whole grain period (P < .001), but overall energy intake from provided foods and non-provided foods did not differ between the two diet periods. Similarly, intake of nutrients and food groups did not differ between the two diets except for dietary fiber and whole grains.
The whole grain diet intervention did not result in any differential changes in markers of glucose metabolism such as fasting glucose or insulin, lipid metabolism, alanine aminotransferase or aspartate aminotransferase levels, satiety based on fasting plasma concentrations of leptin, or systolic or diastolic blood pressure. Additionally, the diet did not result in any significant changes in fecal bacterial species diversity or richness of the microbial community.
However, the whole grain diet reduced body weight (P < .001), sagittal abdominal diameter (P = .001), systemic low-grade inflammatory marker C-reactive protein in serum (P = .003), serum concentrations of proinflammatory cytokines IL-6 (P = .009) and IL1-beta (P = .008), and fat-free mass (P = .01) with a tendency toward reduction in fat mass, compared with the refined grain diet.
“Our results add to a growing body of literature demonstrating the ability of whole grain consumption to reduce low-grade systemic inflammation and body weight,” the researchers wrote. “Here, we found that the reduction in body weight was directly associated with the reduction in energy intake, suggesting that whole grain products, compared with refined grain products, induce satiation at a lower energy intake level. This is in line with a recent study, suggesting that whole grain-induced weight loss is mediated by a lower energy intake.”
Roager and colleagues concluded that they found little evidence in the whole grain diets regarding improved gut microbiota composition.
“We know that diet has a profound effect on our gut bacteria,” Roager told Healio.com/Hepatology. “A change in gut bacteria may be beneficial for some patients. However, I think physicians should be aware that at this stage we do not know which individuals will benefit in terms of a changed gut microbiota from a certain dietary change since it appears that the gut microbiome response to a given dietary change is very personal. Due to this personal ‘nature’ of the gut microbiota, physicians might in the future take the individuals’ gut bacteria into account when discussing lifestyle changes with their patients.” – by Talitha Bennett
Disclosure: Roager reports he received grant and research support from Grifols. Please see the full study for the other authors’ relevant financial disclosures.
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