The Regulation of Circulating Hepatokines by Fructose Ingestion in Humans

The effect of intensive resistance exercise and excessive fructose intake on metabolic and physiological responses

BACKGROUND

Muscle-derived uric acid (UA) precursors combined with fructose ingestion may increase liver UA production. Temporary hyperuricemia could impact metabolic and physiological responses over a 24-h period. This study examined the effects of intensive resistance exercise (RE) combined with excessive fructose intake on metabolic and physiological responses.

METHODS

Twelve healthy young males participated in four trials: RE with fructose intake (EF), RE with water intake (EW), control (no exercise) with fructose intake (CF), and control with water intake (CW). Blood UA, glucose, lipids, blood pressure, and markers of kidney and liver function were measured during fasting and at 0, 0.5, 1, 2, 4, and 24 h before and after exercise.

RESULTS

UA levels in the EF and EW trials were significantly higher than those in the CF and CW trials at all post-exercise time points. The next morning, UA levels in the EF trial remained above 7 mg/dL. Increased glucose levels at 0 and 0.5 h post-exercise and increased creatinine (CRE) levels immediately post-exercise were observed. RE reduced the area under the curve for the estimated glomerular filtration rate (eGFR) and increased systolic blood pressure, mean arterial blood pressure, and the UA/CRE ratio the next morning. Fructose intake increased glutamate pyruvate transaminase (GPT) levels 24 h post-exercise. CRE showed a positive correlation with UA levels, while eGFR was negatively correlated with UA levels in the RE trials. Additionally, GPT levels correlated positively with UA following fructose intake.

CONCLUSION

Intensive RE combined with excessive fructose intake induced a notable increase in UA levels. This increase in UA levels appeared to be associated with temporary fluctuations in markers related to renal function.

Effect of a 6-Week Carbohydrate-Reduced High-Protein Diet on Levels of FGF21 and GDF15 in People With Type 2 Diabetes

Context

Fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) are increased in type 2 diabetes and are potential regulators of metabolism. The effect of changes in caloric intake and macronutrient composition on their circulating levels in patients with type 2 diabetes are unknown.

Objective

To explore the effects of a carbohydrate-reduced high-protein diet with and without a clinically significant weight loss on circulating levels of FGF21 and GDF15 in patients with type 2 diabetes.

Methods

We measured circulating FGF21 and GDF15 in patients with type 2 diabetes who completed 2 previously published diet interventions. Study 1 randomized 28 subjects to an isocaloric diet in a 6 + 6-week crossover trial consisting of, in random order, a carbohydrate-reduced high-protein (CRHP) or a conventional diabetes (CD) diet. Study 2 randomized 72 subjects to a 6-week hypocaloric diet aiming at a ∼6% weight loss induced by either a CRHP or a CD diet. Fasting plasma FGF21 and GDF15 were measured before and after the interventions in a subset of samples (n = 24 in study 1, n = 66 in study 2).

Results

Plasma levels of FGF21 were reduced by 54% in the isocaloric study (P < .05) and 18% in the hypocaloric study (P < .05) in CRHP-treated individuals only. Circulating GDF15 levels increased by 18% (P < .05) following weight loss in combination with a CRHP diet but only in those treated with metformin.

Conclusion

The CRHP diet significantly reduced FGF21 in people with type 2 diabetes independent of weight loss, supporting the role of FGF21 as a "nutrient sensor." Combining metformin treatment with carbohydrate restriction and weight loss may provide additional metabolic improvements due to the rise in circulating GDF15.

Postprandial secretion of follistatin after gastric bypass surgery and sleeve gastrectomy

Follistatin is secreted from the liver and may regulate muscle growth and insulin sensitivity. Protein intake stimulates follistatin secretion, which may be mediated by increased glucagon in the context of low insulin concentrations. We investigated circulating follistatin after mixed-meals in two cohorts of patients who were part of previously published studies and had undergone bariatric surgery with either simultaneous assessment of amino acid absorption or administration of the GLP-1 receptor antagonist exendin-(9-39), which increased glucagon concentrations and impaired insulin secretion. Study 1 comprised obese matched subjects with previous Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgery and unoperated controls who underwent 6-hour mixed-meal tests with intravenous and oral tracers including intrinsically labelled caseinate in the meal. Study 2 comprised obese subjects with previous RYGB who underwent two 5-hour mixed-meal tests with concomitant exendin-(9-39) or saline infusion. In study 1, the secretion of follistatin as well as the amino acid absorption was accelerated after RYGB compared with SG and controls, but the glucagon-to-C-peptide ratios did not differ between the groups. In study 2, exendin-(9-39) administration increased postprandial glucagon concentrations and lowered insulin secretion, whereas the concentration of follistatin was unchanged. In conclusion, postprandial follistatin secretion is accelerated in patients after RYGB which might be explained by an accelerated protein absorption rate rather than the glucagon-to-insulin ratio.