Diets differing in carbohydrate cellularity and amount similarly reduced visceral fat in people with obesity - a randomized controlled trial (CARBFUNC)

Quality and quantity of carbohydrates, faecal short-chain fatty acids and gastrointestinal symptoms - results from a randomised, controlled trial (CARBFUNC)

BACKGROUND & AIMS

Diet is a key determinant of gastrointestinal (GI) health, in part in association with microbiota-derived short-chain fatty acids (SCFAs). However, we need more knowledge of the relative impact of dietary carbohydrate amount and quality on GI symptoms, GI-associated quality of life (QoL) and faecal SCFAs.

METHODS

193 males and females with obesity were randomly allocated to follow one of three isocaloric, iso-proteinic dietary patterns (2000 kcal/day for females, 2500 kcal/day for males): a higher-carbohydrate lower-fat diet with refined carbohydrate sources (acellular diet, A-HCLF, comparator arm), a higher-carbohydrate lower-fat diet with minimally refined carbohydrate sources (intact cellular structures, cellular diet, C-HCLF), or a low-carbohydrate high-fat diet (LCHF), all low in added sugars. Secondary outcomes of this randomised controlled trial (CARBFUNC) were assessed, i.e., changes in abdominal symptoms (irritable bowel syndrome severity scoring system (IBS-SSS)), reflux symptoms (gastro-oesophageal reflux disease questionnaire (GerdQ)), GI-related QoL (Short-Form Nepean Dyspepsia Index (SF-NDI)) and fatigue (Fatigue Impact Scale), and faecal SCFAs concentrations after following the diets for 3 and 12 months. Group differences were analysed by constrained linear mixed effect modelling (cLMM).

RESULTS

118 and 57 participants completed 3 and 12 months of the dietary intervention, respectively, with no significant group differences in weight loss at 12 months (5-7%). At 12 months, the mean daily fibre intake was 34 ± 7 g/day, 41 ± 14.3 g/day, and 18.5 ± 6 g/day on the A-HCLF, C-HCLF and LCHF diet, respectively, compared to 21 ± 7, 21 ± 7 and 20 ± 6 g/day at baseline. We observed no significant between-group difference in IBS-SSS sum score after 3 and 12 months. We found significant improvement in GerdQ score (change score [95 % CI]: -0.62 [-1.18, -0.048], p = 0.034), and SF-NDI sum score (-1.88 [-3.22, -0.52], p = 0.007) after 3 months on the LCHF diet compared to the A-HCLF diet, and GerdQ remained significant at 12 months (-1.03 [-1.88, -0.19], p = 0.017). Compared to the A-HCLF diet, the concentration of faecal butyric acid increased significantly more after 3 months on the C-HCLF diet (4.97 [1.71, 8.23] p = 0.003) and faecal acetic acid decreased more (-6.41 [-12.8, -0.047]. p = 0.048) on the LCHF diet. At 12 months the greater reduction in faecal acetic acid on the LCHF diet remained significant (-9.82 [-19.0, -0.67], p = 0.036), along with significantly greater reductions also in total SCFAs (-21.3 [-38.0, -4.56], p = 0.013), propionic (-4.42 [-7.79, -1.05], p = 0.010), and butyric acid (-5.05 [-9.60, -0.51], p = 0.030).

CONCLUSION

In this sample of adults with obesity and mild GI symptoms at baseline, modest improvements were observed only for the LCHF diet in QoL (at 3 months) and reflux symptoms (at 3 and 12 months), which was significantly different from the acellular carbohydrate diet, and independent of total fibre intake. Concomitantly, compared to the acellular carbohydrate diet, the cellular diet significantly increased the faecal concentration of butyric acid, whereas the LCHF diet lowered acetic acid after 3 months and all the major SCFAs after 12 months.

CLINICAL TRIALS IDENTIFIER

NCT03401970. https://clinicaltrials.gov/ct2/show/NCT03401970.

Randomised controlled trial of lifestyle interventions for abdominal obesity in primary health care

AIM

Assess effects on waist circumference from diet with or without cereal grains and with or without long-term physical exercise.

BACKGROUND

Elevated waist circumference is an indicator of increased abdominal fat storage and is accordingly associated with increased cardiovascular mortality. This is likely due to the association between lifestyle-induced changes in waist circumference and cardiovascular risk factors. Reductions in waist circumference may be facilitated by diet without cereal grains combined with long-term physical exercise.

METHODS

Two-year randomised controlled trial with factorial trial design in individuals at increased risk of cardiovascular disease with increased waist circumference. Participants were allocated diet based on current Swedish dietary guidelines with or without cereal grains (baseline diet information supported by monthly group sessions) and with or without physical exercise (pedometers and two initial months of weekly structured exercise followed by written prescription of physical activity) or control group. The primary outcome was the change in waist circumference.

FINDINGS

The greatest mean intervention group difference in the change in waist circumference among the 73 participants (47 women and 26 men aged 23-79 years) was at one year between participants allocated a diet without cereal grains and no exercise and participants allocated a diet with cereal grains and no exercise [M = -5.3 cm and -0.9 cm, respectively; mean difference = 4.4 cm, 4.0%, 95% CI (0.0%, 8.0%), P = 0.051, Cohen's d = 0.75]. All group comparisons in the change in waist circumference were non-significant despite the greatest group difference being more than double that estimated in the pre-study power calculation. The non-significance was likely caused by too few participants and a greater than expected variability in the change in waist circumference. The greatest mean intervention group difference strengthens the possibility that dietary exclusion of cereal grains could be related to greater reduction in waist circumference.

Diet-microbiota interaction in irritable bowel syndrome: looking beyond the low-FODMAP approach

BACKGROUND

Diet is one of the main modulators of the gut microbiota, and dietary patterns are decisive for gut-microbiota-related diseases, including irritable bowel syndrome (IBS). The low-FODMAP diet (LFD) is commonly used to treat IBS, but its long-term effects on microbiota, symptoms and quality of life (QoL) are unclear. Alternative dietary strategies promoting beneficial gut microbiota, combined with reduced symptoms and improved QoL, are therefore of interest.

AIMS

To review current evidence on the diet-microbiota-interaction as a modulator of IBS pathophysiology, and dietary management of IBS, with particular emphasis on strategies targeting the gut microbiota, beyond the LFD.

METHODS

Literature was identified through PubMed-searches with relevant keywords.

RESULTS

Dietary patterns with a low intake of processed foods and a high intake of plants, such as the Mediterranean diet, promote gut microbiota associated with beneficial health outcomes. In contrast, Western diets with a high intake of ultra-processed foods promote a microbiota associated with disease, including IBS. Increasing evidence points towards dietary strategies consistent with the Mediterranean diet being equal to the LFD in alleviating IBS-symptoms and having a less negative impact on QoL. Timing of food intake is suggested as a gut microbiota modulator, but little is known about its effects on IBS.

CONCLUSIONS

Dietary recommendations in IBS should aim to target the gut microbiota by focusing on improved dietary quality, considering the impact on both IBS-symptoms and QoL. Increased intake of whole foods combined with a regular meal pattern and limitation of ultra-processed foods can be beneficial strategies beyond the LFD.

Relationship between Ketones, Ghrelin, and, Appetite on Isocaloric Diets with Varying Carbohydrate Quality and Amount: Results from a Randomized Controlled Trial in People with Obesity (CARBFUNC)

BACKGROUND

Low-carbohydrate high-fat (LCHF) diets may suppress the increase in appetite otherwise seen after diet-induced fat loss. However, studies of diets without severe energy restriction are lacking, and the effects of carbohydrate quality relative to quantity have not been directly compared.

OBJECTIVES

To evaluated short- (3 mo) and long-term (12 mo) changes in fasting plasma concentrations of total ghrelin, β-hydroxybutyrate (βHB), and subjective feelings of appetite on 3 isocaloric eating patterns within a moderate caloric range (2000-2500 kcal/d) and with varying carbohydrate quality or quantity.

METHODS

We performed a randomized controlled trial of 193 adults with obesity, comparing eating patterns based on "acellular" carbohydrate sources (e.g., flour-based whole-grain products; comparator arm), "cellular" carbohydrate sources (minimally processed foods with intact cellular structures), or LCHF principles. Outcomes were compared by an intention-to-treat analysis using constrained linear mixed modeling. This trial was registered at clinicaltrials.gov as NCT03401970.

RESULTS

Of the 193 adults, 118 (61%) and 57 (30%) completed 3 and 12 mo of follow-up. Throughout the intervention, intakes of protein and energy were similar with all 3 eating patterns, with comparable reductions in body weight (5%-7%) and visceral fat volume (12%-17%) after 12 mo. After 3 mo, ghrelin increased significantly with the acellular (mean: 46 pg/mL; 95% CI: 11, 81) and cellular (mean: 54 pg/mL; 95% CI: 21, 88) diets but not with the LCHF diet (mean: 11 pg/mL; 95% CI: -16, 38). Although βHB increased significantly more with the LCHF diet than with the acellular diet after 3 m (mean: 0.16 mmol/L; 95% CI: 0.09, 0.24), this did not correspond to a significant group difference in ghrelin (unless the 2 high-carbohydrate groups were combined [mean: -39.6 pg/mL; 95% CI: -76, -3.3]). No significant between-group differences were seen in feelings of hunger.

CONCLUSIONS

Modestly energy-restricted isocaloric diets differing in carbohydrate cellularity and amount showed no significant differences in fasting total ghrelin or subjective hunger feelings. An increase in ketones with the LCHF diet to 0.3-0.4 mmol/L was insufficient to substantially curb increases in fasting ghrelin during fat loss.