Intermittent fasting is quickly gaining popularity as a strategy to support weight loss. Typically, people who use this approach restrict their calorie intake to 75-90% of their energy needs on 1 or 2 days per week. However, intermittent fasting is in the ‘slow and steady’ group of weight loss approaches, taking around 24 weeks to achieve modest reductions in weight.
Researchers were curious to understand if the benefits of intermittent fasting could be combined with a calorie restricted diet to achieve faster weight loss results, and to understand if the use of liquid meal replacements impacted on the weight loss and cardiovascular measures of participants.
In order to test this, a trial was conducted amongst 60 obese women recruited from the University of Illinois. Participants were randomised into two groups – the first would combine intermittent fasting with a liquid meal replacement protocol, and the second would combine intermittent fasting with a food-based restricted calorie diet.
The liquid meal replacement group were instructed to consume a breakfast and lunch replacement shake (each 240 kcal) and a 400-600 kcal meal at dinner. The food-based restricted calorie diet group ate 3 meals per day in accordance with the National Cholesterol Education Program Therapeutic Lifestyle Changes diet, structured as 240kcal meals for breakfast and lunch, plus a 400-600kcal dinner. Both groups received weekly education sessions from a registered dietician and sourced and prepared their own food meals.
Both groups ate according to their prescribed diets for 6 days of the week, with a fast on the last day (water consumption plus 120kcal of juice powder). Overall calorie intake for both groups was restricted by 30% of their baseline needs.
The study ran for a total of 10 weeks: for the first two weeks, participants were instructed to eat their usual diet to establish a baseline weight maintenance period. The intervention then ran for 8 weeks. Food records were kept and analysed to understand compliance with the diets for both groups.
Results from the study showed:
- Stable weight amongst both groups during the weight maintenance period
- Improved compliance to the restricted calorie protocol for participants in the liquid meal replacement group: (92% compared with 80% for the participants in the food-based intervention)
- No difference in fast-day compliance between the two groups
- No difference in the macronutrient composition between the two groups during the intervention period
- Average reduction in body weight of 3.9kg in the liquid meal replacement group compared with 2.5kg in the food-based intervention group
- Greater decreases in BMI (1.3 vs 0.8) and fat mass (2.8kg vs 1.9kg) in the liquid meal replacement group than the food-based intervention group
- Greater reduction of total cholesterol, LDL cholesterol, and triglycerides in the liquid meal replacement group.
This study shows how the combination of intermittent fasting plus calorie restriction can impact on weight loss for women who are obese. Importantly, use of liquid meal replacements as part of a calorie-restricted diet can result in better compliance, higher levels of weight loss, greater decreases in BMI and see improvement in some measures of cardiovascular health.
For weight loss consultants, the use of a combined intermittent fasting plus calorie restriction strategy might be best used for people who want to amplify the weight loss they would ordinarily be expected to achieve using intermittent fasting as a weight loss strategy in isolation. In particular, use of liquid meal replacements appears to achieve increased weight loss results compared with other approaches to calorie restriction. The authors of the study note that the long-term effects of this approach should still be tested in a large-scale human trial.
Klempel, M. C., Kroeger, C. M., Bhutani, S., Trepanowski, J. F., & Varady, K. A. (2012). Intermittent fasting combined with calorie restriction is effective for weight loss and cardio-protection in obese women. Nutrition Journal, 11(1), 98.