Intermittent energy restriction (IER) has been an increasingly popular alternative to the more common ongoing energy restriction. It’s believed to have benefits for weight loss, and may have additional benefits for heart health and even insulin resistance.
But does this approach have benefits that equal those of continuous energy restriction (CER)?
Obesity is linked to an increased risk of many cardiometabolic diseases, including cardiovascular disease and type 2 diabetes. Central obesity is of particular concern when it comes to increasing risk of heart disease and diabetes. When looking for ways to address obesity, it may be important to also consider other risk factors for these conditions.
Reviews have reported that IER is no more effective than CER for treating overweight and obesity. However, studies do suggest that IER has benefits for blood pressure, fasting glucose, lipids, inflammatory markers and insulin resistance.
IER diets typically comprise of a period of severe energy restriction, usually for 24-48hrs, followed by a period of habitual energy intake. Some of the approaches that fall under IER include alternate day fasting, and the 5:2 diet – 5 days of unrestricted eating and 2 days of severe energy restriction of 500-600 calories.
To further explore the comparison of IER and CER, researchers designed a study to explore the effect of both approaches on cardiometabolic health.
The study designed was a 4-week parallel-arm randomised controlled trial that compared IER and CER diets and their effect on cardiovascular and metabolic markers on adults with central obesity.
Inclusion criteria were non-smoking adults aged 35-75 with a waist circumference that fell within the World Health Organisation’s definition of high risk for cardiometabolic disease. This was >102cm for men and >88cm for women. For those of South or East Asian descent, it is defined as >90cm for men and >80cm for women.
Exclusion criteria included kidney or cardiovascular disease, cancer, diabetes, chronic liver disease, precious bariatric surgery, significant psychiatric disorders, eating disorders, use of medications that affect metabolic health and/or weight and pregnancy and breastfeeding.
45 participants took part in the study. Both the IER and CER protocols were designed to reduce weekly energy intake by 3500kcal, with the aim of eliciting a 2kg weight loss by the end of the trial. Participants in the CER group were given personalised dietary advice for a Mediterranean-style diet with a daily 500kcal deficit.
In the IER group, participants were asked to follow a very-low calorie diet for 2 consecutive days each week, using meal replacement food packs of 600kcal. On the remaining 5 days, participants were asked to follow a Mediterranean-style diet.
Both groups were given a physical activity goal based on their baseline physical activity levels.
Outcomes measured included insulin sensitivity, blood pressure, heart rate variability and markers of insulin resistance, lipids and inflammation.
Reductions in body weight were equivalent in both groups. Insulin sensitivity testing indicated that there was a similar increase in insulin sensitivity in both groups.
There was a decrease in fasting plasma glucose concentration with the CER group but not IER group. However, the IER group saw a reduction in fasting plasma non-esterified fatty acid concentrations that was not seen in the CER group.
There were no differences noted in lipids, inflammatory markers or heart rate variability between the groups.
The researchers concluded that short-term IER and CER diets are comparable for most cardiometabolic risk factors.
A few limitations were noted. Insulin sensitivity testing was only conducted in a fasting state, which may miss any benefits experienced after consuming a meal. Additionally, the findings cannot be applied to those at higher risk, such as those with hypertension or pre-diabetes, without further research.
Pinto, A.M., Bordoli, C., Buckner, L.P., Kim, C., Kaplan, P.C., Del Arenal, I.M., Jeffcock, E.J. and Hall, W.L., 2019. Intermittent energy restriction is comparable to continuous energy restriction for cardiometabolic health in adults with central obesity: a randomized controlled trial; The Met-IER Study. Clinical Nutrition.