Obesity has reached epidemic proportions. Over 1.9 billion adults and 380 million children are now overweight or obese (1). These people are more likely to suffer from chronic life-threatening diseases such as heart disease, stroke, diabetes and cancer (1). Obesity has become such a widespread problem because of our inactive lifestyle and readily available high-calorie food. The World Health Organization recommends people combat obesity by exercising more, eating more fruit and vegetables, and less fat and processed sugars.
Calorie Restriction Can Help Treat Obesity
Calorie restriction can extend lifespan and delay age-related diseases in animals ranging from worms and flies right through to non-human primates. There is also a lot of interest in how calorie restriction can tackle obesity and improve metabolic health.
Previous clinical studies suggest that intermittent calorie restriction may lead to more fat loss and lower insulin levels than continuous calorie restriction (2). However, it is not clear whether these benefits last longer than six months.
Intermittent vs Continuous Calorie Restriction
To answer this question, German scientists recently conducted a year-long trial of calorie restriction in 150 overweight and obese people. They looked at whether dieting for two days a week was as effective as continuous dieting.
The 52-week trial included a 12-week intervention period, 12-week maintenance period and 26-week follow up period. Researchers asked participants to maintain their diet regime for the whole 52 weeks.
Each week the intermittent dieters could eat their full energy requirement for five days but had to severely restrict calorie intake on two days. On those two days participants could only eat 25% of their individual energy requirement. Researchers calculated energy requirements based on participants’ activity levels. In contrast, continuous dieters could only eat 80% of their individual energy requirement each day. The study also included a control group that had no specific dietary restriction but was told to follow the German Nutrition Society’s guidelines for healthy eating.
During the 12-week intervention period, intermittent and continuous dieters met with dieticians for dietary counseling. Dieticians gave participants in these two groups a personalized diet plan and twice weekly follow up phone calls. The control group did not get the same level of support. All three groups kept food diaries in week one and week 12 of the study. Despite the fact that the control group was not asked to restrict their calorie intake, food diaries showed that all three groups ate more protein, fiber and carbohydrates and less fat and alcohol.
The study authors went on to test whether the diets were working by measuring participants’ body weight, fat content and circulating metabolic biomarkers after the 12-week intervention period and at 50 weeks. They also measured gene expression in participants’ adipose tissue at these time points. The Biobank of the National Center for Tumor Diseases in Heidelberg, Germany processed all samples.
Weight Loss and Better Metabolic Health
After 12 weeks of dieting, the intermittent group had lost an average of 7.1% of their body weight, almost 2% more than the continuous dieters (5.2%) and more than double that of the control group (3.3%). All groups, including the control group, also had significant decreases in metabolic markers, including a 7.5-20% decrease in circulating cholesterol and triglycerides, 6-20% decrease in insulin, 3-7.6% decrease in glucose and 44-48% decrease in leptin. There was no significant difference in metabolic marker levels between any of the groups.
Researchers also tested the expression of 82 genes in the adipose tissue of participants. All of these genes are linked to obesity or chronic diseases like cardiovascular disease. The authors found no difference in any of these genes after the 12-week intervention period.
Participants had gained back some of their weight by the 50-week follow up. At this time point, the intermittent dieters were 5.2% lighter than at the start of the study, compared with the continuous dieters who were 4.9% lighter and the control group who were 1.7% lighter. This overall weight loss correlated with similar changes in abdominal and subcutaneous fat. There was no difference in circulating metabolic markers between the intermittent and continuous dieters at the 50-week follow up.
This study supports previous data showing that intermittent calorie restriction can be as effective as continuous restriction. The difference with this study is that it followed participants for a whole year to see whether they could maintain their diet regime and weight loss. While participants did gain back some of their lost weight during the year, they were still, on average, 5% lighter than at the start of the study. They also had significantly improved metabolic markers such as lower blood glucose levels. The fact that the control group also lost weight and improved their metabolic health during the 12-week intervention period shows that the style of calorie restriction may be less important than having regular follow up with dieticians and other healthcare professionals.