The differential effects of low-carb diet and habitual diet on the fecal level of short-chain fatty acid

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A recent clinical trial report, published in Scientific Reports, compared the fecal levels of short-chain fatty acid (SCFA) and serum inflammatory markers between individuals under a low-carbohydrate (LCD) and a habitual (HD) diet.

Study: A low-carb diet increases fecal short-chain fatty acids in feces of obese women following a weight-loss program: randomized feeding trial.Image Credit: Boontoom Sae-Kor/Shutterstock.comStudy: A low-carb diet increases fecal short-chain fatty acids in feces of obese women following a weight-loss program: randomized feeding trial.Image Credit: Boontoom Sae-Kor/Shutterstock.com

Background

Diet plays an important role in maintaining health. For instance, the Western-style diet has been associated with increased inflammation and gut microbial dysbiosis that promotes obesity and causes a reduction in the abundance and diversity of beneficial microbes, such as Bifidobacterium sp. and Lactobacillus sp. In contrast, the Mediterranean diet enhances beneficial gut microbiota and promotes healthy life.

Obesity has been recognized as one of the leading causes of all chronic diseases. Previous studies have shown that obesity has increased due to high consumption of high-fat and high-carbohydrate diets worldwide.

The high prevalence of obesity has led to the health system's development of many safe and effective anti-obesity strategies.

Varied dietary interventions have shown various effectiveness in treating obesity and overweight. This variable efficacy has been linked with many factors, including adherence and nutrient levels.

A low-carbohydrate diet, popularly called a low-carb diet, is a popular dietary intervention for rapid weight loss. However, the effectiveness of this diet for weight reduction differs due to variable carbohydrate content and quality. This variability presents the difficulty of assessing the true effect of a low-carb diet on obesity.

Effective alterations of dietary fatty acids have been linked to preventing metabolic complications, typically induced by a high-fat diet. Compared to mono- and polyunsaturated fatty acids (MUFAs and PUFAs), saturated fatty acids (SFAs) are more obesogenic. This is because a diet rich in MUFAs and PUFAs generates greater thermogenesis than SFAs.

Studies have indicated that a low-carb diet improves blood glucose, serum insulin levels, and blood pressure in obese patients. Furthermore, this diet positively affects the homeostasis model assessment of insulin resistance (HOMA-IR).

SCFAs are synthesized by gut microbes using undigested/unabsorbed dietary components. Due to their role in the gut barrier, SCFAs have recently gained much attention. 

About the study

The current study hypothesized that SCFAs, produced by gut microbiota, alter with changes in the microbiota composition. This study compared the effect of LCD and HD on fecal levels of SCFAs and inflammatory markers in obese women.

Acetate, propionate, and butyrate are the three main SCFAs synthesized by the gut microbiome, existing in 60:20:20 molar ratios in the colon and stool. However, their content depends upon the diet and gut microbiota diversity. 

This study used a block randomization strategy, where the randomization unit was participants. Here, five blocks of four participants each were considered.

Study findings

At baseline, no significant difference in total fat, protein, calorie, carbohydrate, and fiber content was observed between the two study groups, i.e., the LCD and HD.

However, at the end of the study period, a significant difference in weight and waist circumference (WC) was observed in both dietary groups. It must be noted that the mean changes in WC and weight were not statistically significant between the two study groups.

A significant decrease in the waist-to-hip ratio (WHR) was observed compared to baseline readings in both study groups. However, the mean change of WHR was significantly higher in the LCD group. Regarding metabolic markers, a greater reduction in serum insulin and HOMA-IR was observed in the HD group compared to the LCD group.

A serum inflammatory marker assessment revealed a significant decrease in serum interleukin-6 (IL-6) in the HD group compared to the baseline estimations. After the intervention, both groups significantly reduced serum high-sensitive C-reactive protein (hs-CRP) levels. 

The serum hs-CRP level was observed to affect the fecal level of butyric acid significantly. An increase in serum hs-CRP leads to a reduction in the percentage of fecal butyric acid by 25%.

Fecal propionic acid influences butyric acid levels. Furthermore, the serum insulin level significantly increases the fecal level of acetic acid, i.e., by 8.9-fold. Both fecal propionic and butyric acid influence acetic acid.

The gut microbial characterization revealed no significant difference in Firmicutes and Bacteroidetes levels in LCD and HD groups before and after the intervention. At the end of the intervention, the number of positive-Actinobacteria participants was higher in the LCD group than in the HD group.

After six months of intervention, fecal acetic acid, butyric acid, and propionic levels significantly increased in both dietary groups. However, these levels were higher in the LCD group compared to the HD group. 

Conclusions

The current study revealed that a low-carb diet enhances fecal SCFAs after a month-long weight loss program. In the future, more research is required to elucidate the underlying mechanisms of these changes and human health outcomes.

Journal reference:
Dr. Priyom Bose

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.

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