A carbohydrate-restricted diet for patients with irritable bowel syndrome lowers serum C-peptide, insulin, and leptin without any correlation with symptom reduction
Starch and sucrose-reduced diet led to lower levels of C-peptide, insulin and leptin
Reduction of C-peptide and insulin levels correlated with reduced carbohydrate intake
There was no correlation between hormone levels and gastrointestinal symptoms
Alterations in gut endocrine cells and hormone levels have been measured in patients with irritable bowel syndrome (IBS). The hypothesis of the present study was that hormone levels would change after 4 weeks of a starch- and sucrose-reduced diet (SSRD) intervention corresponding to decreased carbohydrate intake and symptoms. Among 105 IBS patients from primary and tertiary healthcare, 80 were randomized to SSRD, while 25 followed their ordinary diet. Food diaries, Rome IV, and IBS-symptom severity score (IBS-SSS) questionnaires were completed, and blood samples were collected at baseline and after the intervention. Serum C-peptide, gastric inhibitory peptide, glucagon, glucagon-like peptide-1, insulin, leptin, luteinizing hormone, polypeptide YY, and glucose were measured, along with the prevalence of autoantibodies against gonadotropin-releasing hormone; its precursor, progonadoliberin-2, and receptor; and tenascin C. Carbohydrate intake was lower in the intervention group than in controls at week 4 (median: 88 [66-128] g vs 182 [89-224] g; P < .001). The change in carbohydrate intake, adjusted for weight, was associated with a decrease in C-peptide (β: 14.43; 95% confidence interval [CI]: 4.12-24.75) and insulin (β: 0.18; 95% CI: 0.04-0.32) levels. Glucose levels remained unchanged. The IBS-SSS scores were lower in the intervention group but not in controls (P < .001), without any association with changes in hormone concentrations. There was no difference in autoantibody prevalence between patients and healthy controls. In conclusion, the hypothesis that reduced carbohydrate intake corresponded to altered hormonal levels in IBS was accepted; however, there was no relationship between hormonal concentrations and symptoms.
Keywords: Carbohydrate-restricted diet; Dietary intervention; Gonadotropin-releasing hormone; Hormones; Irritable bowel syndrome; Starch- and sucrose-reduced diet.
Patients randomized to the intervention group (n = 80) received dietary advice that mainly focused on starch and sucrose reduction, while increasing intake of fruits and vegetables with less starch content, egg, fish, meat, and dairy products. The dietary advice was similar to that given to patients with congenital sucrase-isomaltase deficiency (CSID) . Briefly, all kinds of sucrose-containing food, e.g., sweets, cakes, jam, and juice, were to be avoided, and snacks should be replaced with nuts. Regular carbohydrates, such as processed rice and pasta, were discouraged and instead fiber-rich alternatives, such as raw rice, fiber-rich pasta, and fiberrich bread, were recommended. Patients were provided with visual aids to familiarize themselves with which berries, fruits, legumes, and vegetables to prefer or avoid (Table 1). Increased fat and/or protein intake was recommended to delay gastrointestinal transport and promote starch tolerance. Patients were encouraged to prolong chewing during food intake and chew food completely to enhance salivary amylase breakdown of starch. The dietary intervention did not focus on overall frequency or regularity of feeding habits. The patients randomized to the control group (n = 25) were recommended to continue with their ordinary food habits. All participants were encouraged to continue with their ordinary degree of physical activity and medications. The participants could reach the study staff by telephone or email whenever they wanted during the study.
The carbohydrate intake in the control and intervention groups was equal at baseline (Table 4, Figure 3a), but significantly lower in the intervention group than in the control group at week 4 (88 [66–128] g versus 182 [89–224] g, P < .001) (Table 4, Figure 3a). The changes during the 4-week study differed between the groups (P < .001) (Figure 3b)
There were no significant differences in the scores for abdominal pain, days of pain, bloating, satisfaction with bowel habits, influence on daily life, and total IBS-SSS scores between the two groups at baseline (Table 4). After 4 weeks, the patients on the SSRD diet had significantly improved scores for the individual questions and total IBS-SSS scores, which was not observed in the control group (Table 4). The changes in total IBS-SSS scores differed between the intervention and control groups (-148 [-203– -72] versus -30 [-54–33], P < .001).
3.3 Hormonal levels
At baseline, glucagon levels were significantly higher in the intervention group than in the control group (33.9 [26.4–58.6] pM versus 27.0 [18.9–36.3] pM, P = .03) (Table 6). Glucagon levels remained significantly higher (38.0 [26.3–70.2] pM versus 28.9 [22.3–41.4] pM, P = .02) and leptin levels were significantly lower (10531.9 [4776.4–25081.1] pg/mL versus 28074.7 [12623.0–41315.3] pg/mL, P = .01) in the intervention group than in the control group after 4 weeks (Table 6). Levels of C-peptide (Figure 4a), GIP (Figure 4b), insulin (Figure 4e), and leptin (Figure 4f) were significantly reduced in the intervention group after the dietary intervention compared with those at baseline, whereas there were no changes in the control group (Table 6, Figure 4). The differences in the changes in the levels of C-peptide (P = .03), insulin (P = .03), and leptin (P < .001) between the two groups were significant (Figure 5). There were non-significant differences in the basal hormonal serum levels and changes in levels between IBS subgroups and sexes (data not shown). 3.4 Comparison of hormonal levels with carbohydrate changes and IBS symptoms The decrease in carbohydrate intake correlated with decreased levels of C-peptide (rs = 0.275, P = .02) and insulin (rs = 0.244, P = .04) but not with leptin levels (rs = 0.125, P = .30). To adjust for weight changes, analyses were continued with linear regression. A decrease in carbohydrate intake was associated with a decrease in C-peptide (β: 14.43; 95% CI: 4.12– 24.75) and insulin (β: 0.18; 95% CI: 0.04–0.32), but not leptin (Table 7). The changes in weight were associated with a reduction in C-peptide (β: 493.13; 95% CI: 14.62–971.64), insulin (β: 8.20; 95% CI: 1.71–14.70), and leptin (β: 2346.00; 95% CI: 244.75–4447.26) levels. The standardized β value for C-peptide was higher for carbohydrate changes (0.32) than for weight reduction (0.24) but was similar regarding insulin levels (0.29 for both). There were no significant associations with the changes in hormones and carbohydrate intake in the control group (Table 7). There was no correlation between the levels of any hormone and gastrointestinal symptoms, satisfaction with bowel habits, or influence of the gastrointestinal symptoms on daily life at baseline, and the changes in hormone levels did not correlate with any changes in any IBSSSS scores (data not shown).
Our first hypothesis that a SSRD diet would affect serum levels of hormones involved in glucose homeostasis or gut function was partly accepted, since the SSRD led to lower serum levels of the hormones C-peptide, insulin, and leptin in IBS patients, without affecting glucose levels. Our second hypothesis was also partly accepted since the reduction in the serum levels of C-peptide and insulin correlated with a reduction in carbohydrate intake. However, the hypothesis that the changes in hormonal levels would correlate with changes in gastrointestinal symptoms was rejected. No significant differences were observed in the prevalence of IgM autoantibodies against GnRH1, progonadoliberin-2, GnRH-R, or TNC between IBS patients and healthy controls. The use of dietary interventions to manage IBS is common , albeit with debatable efficacy for some diets . A diet with reduced FODMAPs content has been documented to improve the gastrointestinal symptoms experienced by IBS patients in many previous studies [5,30]. The first pilot study examining the SSRD showed a positive effect of the diet on gastrointestinal symptoms in IBS [17,18]. This study showed that SSRD reduced the serum levels of C-peptide and insulin, corresponding with the reduction in carbohydrate intake. C-peptide is important in the biosynthesis of insulin, while insulin regulates the utilization of glucose . Elevated levels of C-peptide and hyperinsulinemia have been found in IBS patients, which is considered to be a consequence of heightened stress-induced cortisol production [31,32] but may also be a consequence of an unhealthy diet . As these hormones are fundamental in glucose homeostasis, their manipulation could possibly provide a platform for the prevention of metabolic syndromes in IBS patients [34,35,36]. Sustained hyperinsulinemia results in insulin resistance, which is a known risk factor for type 2 diabetes and other metabolic syndromes [34,36]. Gulcan et al.  reported that IBS patients have a significantly higher frequency of prediabetes, a risk factor for type 2 diabetes, than healthy controls. Therefore, the prevalence of hyperinsulinemia, type-2 diabetes, and metabolic syndromes should be further examined in IBS patients. The lowered leptin levels were associated with weight reductions, which is in line with the role of leptin in the regulation of energy intake . The secretion of gut hormones is mainly influenced by luminal contents, i.e., the nature of ingested food and food composition [4,37], and regulated by the brain-gut signaling axis . However, the specific mechanisms by which gastrointestinal luminal contents activate the secretion of gut hormones are not fully understood . Nonetheless, these hormones mediate activities in the gut such as gastrointestinal motility, secretion, and permeability [9,39]; as such, alterations in their secretion may contribute to the experience of abnormal gastrointestinal symptoms [4,5]. Studies have found that IBS patients have altered expression of endocrine cells producing hormones, such as cholecystokinin, GIP, secretin, and PYY, in the gut and altered levels of circulating leptin [40,41]. Besterman et al.  demonstrated different levels of plasma gut hormones in different IBS categories, although no specific pattern could be identified. El-Salhy et al.  summarized how different IBS subtypes present with different densities of endocrine cells in the gastrointestinal tract. In the present dietary study, we found a decreased secretion of GIP in the intervention group after 4 weeks, although the changes were not statistically significant compared with those in the control group. We could not confirm any relationship between gastrointestinal symptoms and levels of gut hormones. Furthermore, the present study did not yield any significant differences between subgroups of IBS patients. Thus, the significant role of gut hormones in IBS described by El-Salhy et al. [4,5] may rather be related to the dietary intake than to the symptoms. Nevertheless, IBS patients are likely to benefit from dietary management, and reduced carbohydrate intake presents a promising future dietary strategy [11,12,17,18]. We were unable to confirm the increased prevalence of IgM autoantibodies against GnRH1, progonadoliberin-2, GnRH-R, and TNC in the current cohort of IBS patients, in contrast to what has previously been demonstrated in IBS patients from a tertiary Department of Gastroenterology [2,15]. In the present study, 73% of IBS patients were recruited from PCC. The expression of these antibodies is supposed to be a consequence of neuronal damage to the ENS, exposing GnRH1 and LH to the immune system [2,43]. It is well described that the general IBS population at PCC are different from those referred for further examination by gastroenterology specialists . Factors like impaired psychological well-being , unhealthy diet , and poor lifestyle habits  greatly affect gastrointestinal function and can induce negative experiences similarly to those described as IBS-like symptoms. Therefore, a prudent examination of these patients at PCC is important to confirm the existence of a true gastrointestinal diagnosis. Several patients recruited from Departments of Gastroenterology with non-organic symptoms may suffer from enteric neuropathy rather than IBS . This study emphasizes the difficulty and unreliability of using neuropeptides and immune response mediators as biomarkers for IBS disease, as has been observed in other studies [41,47]. Due to lifestyle and dietary changes over time, metabolic syndromes are on the rise in the general population [34,48], which has placed a great economic burden on society . A carbohydrate-restricted diet has been shown also to decrease hormone levels and gastrointestinal symptoms in type 2 diabetes without any correlations between these decreases . It is therefore necessary to initiate preventive health measures, such as dietary interventions like SSRD and other well-established diets, to reduce the intake of processed sugars and carbohydrates not only in IBS patients but also in those at a risk of metabolic syndromes [34,48]. The strengths of this study include the inclusion of eight hormones and use of robust laboratory technologies for hormonal analyses. In addition, confounders, such as differences in age, weight, and sex, were considered in the analyses when comparing the intervention and control groups in the study. The use of a nutritionist and computer program to analyze the carbohydrate consumption based on patients’ food diaries to give objective data was also a strength of the study.
There are several limitations; one such limitation is the measurement of hormones and glucose in non-fasting serum. The choice not to have fasting visits was to make it easier for patients to come to visits in relation to their working times. However, patients came at approximately the same time for both visits and they were compared with themselves. Another limitation is that not we did not control for factors, such as psychological well-being, and lifestyle influences other than the diet, which could possibly also influence the relationship between IBS and neuropeptides. Furthermore, there was one patient who had been treated for type 2 diabetes. Other limitations are that there was no control cohort for comparison of hormone levels with the general population or subjects without IBS, and only serum levels of hormones were examined and not the expression of endocrine cells in the bowel. In conclusion, a diet focusing on the reduction of starch and sucrose is a promising management approach for the disorder and reduces the highlighted risk of metabolic diseases in IBS patients. The changes in circulating levels of C-peptide and insulin correlate with the changes in carbohydrate intake. Although the role of hormones in the pathophysiology of IBS has been proposed, the explicit link and effect between these hormones have and symptomatology remains to be adequately demonstrated. With regards to the low prevalence of autoantibodies in IBS patients from PCC, further research is required to verify whether patients who present to gastroenterology specialist clinics with IBS-like symptoms are more likely to be suffering from enteric neuropathies unlike those who present to PCCs.
CRediT author statement
Khadija Saidi: Formal analysis, Investigation, Writing – Original draft, Visualization.
Clara Nilholm: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing- Review & Editing.
Bodil Roth: Conceptualization, Methodology, Investigation, Resources, Writing- Review & Editing, Supervision.
Bodil Ohlsson: Conceptualization, Methodology, Investigation, Writing- Review & Editing, Supervision, Project administration, Funding acquisition
Figure 3. a) Comparisons in carbohydrate (CHO) intake (g) at baseline and at 4 weeks after introduction of a starch- and sucrose-reduced diet intervention in the control (n = 25 and n = 22, respectively) and intervention (n = 78 and n = 74, respectively) groups (Wilcoxon paired test). b) Comparisons of the changes in carbohydrate intake between the control (n = 22) and intervention (74) groups (Mann-Whitney U test). P < .05 was considered statistically significant.
Figure 4. Comparisons between hormonal levels at baseline and at 4 weeks (wks) after the introduction of a starch- and sucrose-reduced diet intervention, separated into the control (n = 25 23) and intervention (n = 72) groups. a) C-peptide (pg/mL), b) gastric inhibitory peptide (GIP) (pg/mL), c) glucagon-like peptide-1 (GLP-1) (pM), d) glucagon (pM), e) insulin (µIU/mL), f) leptin (pg/mL), g) luteinizing hormone (LH) (µIU/mL), and h) polypeptide YY (PYY) (pg/mL). Hormones were analyzed using electro-chemiluminescence . Wilcoxon paired test. P < .05 was considered statistically significant.
Figure 5. Differences in the changes between 4 weeks and baseline in the levels of a) Cpeptide (pg/mL), b) insulin (µIU/mL), and c) leptin (pg/mL) in the control (n = 23) and intervention (n = 72) groups after the introduction of a starch- and sucrose-reduced diet intervention. Hormones were analyzed using electro-chemiluminescence . Mann-Whitney U test. P < .05 was considered statistically significant.