Low-GI Mediterranean diet boosts quality of life but not sleep in diabetes-prone adults

In a recent study published in The Journal of Nutrition, researchers examined the effects of low- and high-glycemic-index (GI) Mediterranean-style (MED) healthy eating patterns (HEPs) on sleep and health-related quality of life (HRQoL).

Study: Low- vs high-glycemic index Mediterranean-style eating patterns improved some domains of health-related quality of life but not sleep in adults at risk for type 2 diabetes: The MEDGICarb randomized controlled trial. Image Credit: Aeril / Shutterstock

HRQoL strongly predicts morbidity and mortality and is an important measure to examine the effects of subjective treatment with interventions. Evidence suggests associations between low HRQoL and higher cardiometabolic risks. The 36-item short-form health survey (SF-36) is commonly used to measure HRQoL. Sleep is an important lifestyle factor related to cardiometabolic health and HRQoL.

Various studies have reported associations between adherence to HEPs and subjective measures of well-being and health. Several studies have demonstrated associations between MED-HEP adherence and improved sleep and HRQoL; however, most studies have been cross-sectional, warranting more robust intervention studies.

The GI of food represents its carbohydrate quality, and glycemic variability is a marker of blood glucose fluctuations. Previously, the authors reported that the GI of a MED-HEP is a determinant of glycemic variability and postprandial glucose response. To date, no intervention study has investigated the effects of GI on HRQoL in people with higher cardiometabolic risk.

About the study

In the present study, researchers investigated the effects of low- and high-GI MED-HEPs on sleep and HRQoL among subjects with features of metabolic syndrome. This study was part of a multicenter, randomized controlled trial (MedGICarb) conducted between January 2018 and March 2020 in Sweden, Italy, and the United States (US). The trial involved a three-week baseline period and a 12-week intervention period.

Older and middle-aged adults with two or more two metabolic syndrome features were recruited. One feature was abdominal obesity, and the other was any of the following: elevated blood pressure, fasting plasma glucose, fasting triglycerides, or lower high-density lipoprotein cholesterol. Individuals with cardiovascular events or acute illness within the past six months, anemia, diabetes, liver or renal failure, pregnancy, intensive physical activity, or smoking were excluded.

During the intervention, participants consumed a controlled weight-maintenance diet along the MED-HEP with high or low GI. Questionnaires were administered at baseline and during the last two weeks of the intervention to evaluate subjective measures of sleep and HRQoL. Subjects were instructed to maintain their habits and physical activity during the intervention.

During the baseline period, participants continued their usual, unrestricted diets. However, during the intervention, both groups consumed a MED-HEP with the exact quantities of fiber and carbohydrate, with group-specific diets had distinct starch sources to attain the GI difference. Only half of the carbohydrate intake differed between groups, while the other half was the same.

SF-36 version 2 was used to measure HRQoL. The Pittsburgh Sleep Quality Index (PSQI) examined the effects on sleep quality. Additionally, the Epworth Sleepiness Scale (ESS) was used to evaluate daytime sleepiness. A three-way analysis of variance compared group differences in sleep and HRQoL between baseline and post-intervention periods.

Findings

Overall, 73 and 87 participants in the low—and high-GI groups, respectively, completed the intervention. Of these, 98 completed the ESS, and 150 completed the PSQI and SF36 questionnaires. At baseline, the well-being and health of subjects who completed the intervention were better or similar to those of the general American population for aggregated mental and physical components of HRQoL.

Regarding sleep, 57% of participants had poor sleep quality, and 18% reported excessive daytime sleepiness. Both groups had increased their protein, fiber, carbohydrate, and energy intake and decreased fat and alcohol consumption compared to baseline. The intervention resulted in changes in HRQoL between groups, mainly driven by improvements in the role of physical and vitality domains in the low-GI group.

There were no differences between groups in other HRQoL domains. Moreover, both groups significantly improved general health and vitality domains between baseline and post-intervention periods. No differences were observed between groups in sleep quality, albeit both had improved sleep latency and daytime dysfunction.

Conclusions

The findings revealed that a low-GI MED-HEP resulted in modest improvements in specific HRQoL domains, such as vitality and physical role, relative to a high-GI MED-HEP; furthermore, there were no significant differences in sleep indices between groups. Notably, the study population was primarily Caucasian, limiting generalizability to other ethnic groups. Together, the results suggest that consuming low-GI foods along a MED-HEP may lead to additional benefits in some aspects of self-perceived health.