Intermittent Fasting and Weight Loss – Do the Studies Line Up?
Intermittent fasting (IF) continues to be a hot topic for dietitians and their clients. The PEN Team was pleased to add new content on IF to the PEN® System in November 2021:
Even though this PEN content was a very recent update, a newer randomized controlled study (1) was found. The newer study looked at lean individuals (1), while the recently updated PEN evidence (2) focused on the effects of IF on weight loss with individuals who had weights in the overweight or obesity categories (defined by BMI). The PEN Team thought it might be of interest to readers to compare results for the different populations studied between the newer study and published PEN updated content.
What was the study about?
Lean (i.e. BMI 20-25), healthy individuals in this RCT were randomized to one of three experimental conditions for three weeks (1). The primary intervention examined energy-restricted, alternate-day, 24-hour fasting with 150% energy intake on alternate days for three weeks (0:150, n=12). Control groups involved:
- a matched degree of energy restriction without fasting (75% energy intake daily, 75:75, n=12) or
- alternate-day fasting without energy restriction (fasting and 200% energy intake on alternate days, 0:200, n=12).
The researchers then examined weight changes, body composition, components of energy balance and postprandial metabolism.
What did the authors find?
The authors found that alternate-day fasting with energy restriction to 75% (i.e. 0:150) reduced body fat mass less than the same degree of energy restriction (i.e. 75:75) but with less fat loss (1). There were no fasting-specific effects on metabolic regulation or cardiovascular health. In particular, daily energy restriction (75:75) reduced body mass (-1.91±0.99 kilograms) mostly due to fat loss (-1.75±0.79 kilograms). Restricting energy intake via alternate-day fasting (0:150) also decreased body mass (-1.60±1.06 kilograms, P=0.46 versus 75:75) but with less reduction in body fat (-0.74±1.32 kilograms, P=0.01 versus 75:75). Fasting without energy restriction (0:200) did not reduce either body mass (-0.52±1.09 kilograms; P≤0.04 versus 75:75 and 0:150) or fat mass (-0.12±0.68 kilograms, P≤0.05 versus 75:75 and 0:150). Hormone, cardiometabolic health indices (plasma glucose, insulin, non-esterified fatty acids, glycerol, total cholesterol, high and low density lipoprotein cholesterol, plasma leptin, adiponectin and ghrelin) and subcutaneous adipose tissue gene expression did not change differently between groups (P>0.05).
Are the outcomes/recommendations in the newer study different from the recommendations in the PEN System?
While the sample sizes are small, this study (1) supports the PEN System findings (3) on time-restricted eating regarding concerns about loss of lean mass, as the findings were the same. Intermittent fasting achieved similar weight loss, glycemia, insulin resistance, blood lipids and blood pressure in people who have body mass indices >25 (2).
With the focus of IF on the timing of eating rather than on which foods are eaten, some individuals may or not achieve a desirable diet quality when following an IF eating pattern (2). Dietitians can support clients who are interested in IF by providing client-centred counselling that focuses on healthful and mindful habits including (4,5):
- Eating a variety of foods including vegetables, fruit, whole grains and protein foods.
- Staying hydrated, with water as the drink of choice.
- Engaging in regular physical activity.
- Templeman I, Smith HA, Chowdhury E, Chen YC, Carroll H, Johnson-Bonson D, et al. A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults. Sci Transl Med. 2021 Jun 16;13(598):eabd8034. Abstract available from: https://pubmed.ncbi.nlm.nih.gov/34135111/
- Dietitians of Canada. What are the effects of intermittent fasting compared to an energy-restricted diet on weight loss, body composition, cardiometabolic outcomes and quality of life? In Practice-Based Evidence in Nutrition® [PEN]. 2021 Nov 26. Available from: https://www.pennutrition.com/KnowledgePathway.aspx?kpid=15329&pqcatid=146&pqid=29135. Access only by subscription. Click Sign Up on PEN login page.
- Dietitians of Canada. What are the effects of time-restricted eating compared to a three meal a day eating pattern on weight loss, body composition, cardiometabolic outcomes and physical activity? 2021 Nov 26. Available from: https://www.pennutrition.com/KnowledgePathway.aspx?kpid=15329&pqcatid=146&pqid=29136
- Obesity Canada. Medical nutrition therapy. 2021. Available from: https://obesitycanada.ca/guidelines/nutrition/
- Health Canada. Canada’s Dietary Guidelines. 2019. Available from: https://food-guide.canada.ca/en/guidelines/