In-Depth Review: Excess Adiposity and Disease
Review Article
Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings
Introduction
At present, 35% of adults older than 20 years in the United States have prediabetes.1 If no lifestyle changes are made to improve health, 15%–30% of these individuals will develop type 2 diabetes within 5 years.1 A key strategy to prevent the progression of prediabetes to type 2 diabetes is weight loss.2 Accumulating evidence suggests that even modest weight loss (5%–7% of initial weight) helps to improve several diabetes risk parameters, including fasting glucose, insulin, and insulin sensitivity.[3], [4]
Daily calorie restriction (CR) regimens are still the most common diet strategies implemented for weight loss.5 CR regimens involve reducing energy intake every day by 20%–50% of needs.5 Although CR is effective for weight loss in some individuals, many people find this type of dieting difficult, as it requires vigilant calorie counting on a daily basis.6 People also grow frustrated with this diet, as they are never able to eat freely throughout the day. In light of these issues with CR, another approach termed intermittent fasting (IF) has shown promise in achieving weight loss goals.7 IF differs from CR, in that it only requires an individual to restrict energy 1–3 d/wk, and allows for ad libitum food consumption on the nonrestriction days.7 Alternate day fasting (ADF) is a subclass of IF, which consists of a “fast day” (75% energy restriction) alternating with a “feed day” (ad libitum food consumption). Recent reviews suggest that IF and ADF are equally as effective as CR for weight loss cardioprotection.[7], [8] What has yet to be elucidated, however, is whether IF and ADF elicit comparable improvements in diabetes risk indicators, when compared with CR. Accordingly, the goal of this review was to compare the effects of IF and ADF with daily CR on body weight, fasting glucose, fasting insulin, and insulin sensitivity in overweight and obese adults.
Section snippets
Methods
We performed a systematic search in MEDLINE PubMed using the following search strings: (1) “intermittent fasting and weight loss,” (2) “alternate day fasting and weight” or “alternate day calorie restriction,” (3) “calorie restriction and weight loss and insulin,” (4) “caloric restriction and weight loss and obesity,” and (5) “calorie restriction and metabolic syndrome.” Two reviewers (A.B. and K.H.) separately screened the abstracts for inclusion and exclusion. Full text articles were
Body Weight and Visceral Fat Mass
Obesity is a well-established risk factor for the development of type 2 diabetes. Findings from the Nurses' Health Study demonstrate a 100-fold increase in diabetes risk over 14 years in those with a BMI >35 kg/m2 compared with normal weight individuals.11 At least one contributing factor to insulin resistance that occurs in obesity is the decrease in insulin-mediated peripheral glucose uptake.12 Weight loss results in substantial reductions in insulin resistance, with every 1 kg lost
Glucose and Insulin
Individuals are categorized as having “prediabetes” when (1) fasting glucose falls between 100 and 125 mg/dL, (2) plasma glucose falls between 140 and 199 mg/dL 2 after an oral glucose tolerance test, or (3) hemoglobin A1c falls between 5.7% and 6.4%.34 Lifestyle modification, namely dietary changes and exercise with the goal of weight loss, are commonly used as the first line therapy. Randomized, controlled trials have shown that with intensive dietary counseling and increased physical
Insulin Sensitivity
Insulin resistance is seen in virtually all patients with type 2 diabetes and occurs early in the disease, before overt diabetes is diagnosed. Both a decrease in insulin sensitivity and insulin deficiency are thought to contribute to type 2 diabetes. Interventions directed at reducing body weight have shown promise for improving insulin sensitivity, and have also been shown to delay or prevent onset of type 2 diabetes.38
Body weight and visceral fat mass
Findings from the present review indicate that CR produces slightly superior weight loss when compared with IF/ADF after similar durations of treatment. For instance, after 3–24 weeks of IF or ADF, 3%–8% reductions in body weight were observed. As for CR, 6–24 weeks of diet produced reductions ranging from 4% to14%. Not surprisingly, greater degrees of energy restriction and longer treatment durations produced larger reductions in body weight. IF, ADF, and CR appear to be effective for reducing
Conclusions
In sum, IF, ADF, and CR regimens appear to be effective for reducing body weight, although CR may result in slightly greater weight loss. As for visceral fat mass, and fasting insulin and insulin sensitivity, the effect of IF, ADF, and CR on these diabetic risk parameters appears comparable. Whether these regimens are effective for glucose lowering remains uncertain, and warrants further investigation. Although these preliminary findings show promise for the use of IF and ADF as alternatives to
Acknowledgments
This work was funded by grants from the National Institutes of Health (NIDDK T32DK080674, NHLBI 1R01HL106228-01).
Conflict of interests: None.
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