When I was helping my mother-in-law move from her apartment I came across this 1963 booklet, “Calorie Counter for 6 Quick Weight Loss Diets.” (My mother-in-law tends to hang on to things for a long time!) The 6 weight loss diets featured were the:
- Three-Day Jet Diet
- Seven-Day Hurry Up Diet
- Get Slim Diet
- Stay Young Diet
- Slow-and-Easy Diet (editorial note, seems odd that this one is a “quick weight loss” scheme)
- For Men Only Diet (second editorial note, this diet plan implies that the other five plans are for women).
Diets come and go, but overweight and obesity continue. Today’s popular diet plans are packaged not as diets, but as “lifestyles.” Keto, Paleo, Gluten-free, and Whole 30 are 2018’s versions of “Get Slim” and “Stay Young” diets of the 1960s.
But, the plan I am asked about most often is Intermittent Fasting (IF). There are several versions, but the original plan was popularized by British journalist and physician, Michael Mosley in 2013 (revised and updated in 2015). The book suggests intermittent fasting for 2 days each week (500 calories for women and 600 calories for men) as a weight loss strategy and as a path to improved health. Many of my 50+ friends express interest in this approach because it appears to be an easy way to lose weight.
The premise of the book is that “fasting” on a “5:2” plan (5 days of normal eating and 2 days of fasting) can help achieve a weight loss of 1 or more pounds per week and reduces the risk of chronic disease. The fasting days do not have to be consecutive to follow the diet.
It promises weight loss and protection against cardiovascular diseases and cancer.
Since the book’s publication, researchers have been interested to learn if the promises hold up. Many of the studies are done on rodents and the human studies are mostly short-term. But, there are some pros:
- Reducing calories for 2 days each week could result in weight loss if calories are held constant on non-fasting days. This could be an easy diet for those who have trouble with portion control and it could help individuals jump start a weight loss plan.
- It can help educate dieters on how many calories are in their favorite foods, as they learn how little food it takes to achieve 500 and 600 calories on the fasting days. A man could blow his entire 600 calorie allotment on a Smoothie King Peanut Power Plus Chocolate drink and a woman would have a mere 100 calories left for the day if she drank a Venti Pumpkin Spice Latte at Starbucks.
- There may be some mood enhancement with intermittent fasting. Many cultural and religious practices encourage intermittent fasting (although intermittent fasting is defined as 200-500 calories for a period of 7 to 21 days in one comprehensive review). Mood enhancement is reported when individuals fast intermittently and some chronic inflammatory degenerative disease symptoms, such as rheumatoid arthritis symptoms, appear to be reduced with fasting.
The cons of the diet:
- While the authors claim the diet results in weight loss and reduces disease, there is no evidence to support those claims for this type of intermittent fasting. Some studies show reduced blood sugar and insulin levels, but we don’t know if that translates into eliminating diabetes or heart disease or cancer.
- There is no guarantee that dieters will hold food intake constant and not eat more calories on non-fasting days.
- This plan is also not recommended for pregnant or lactating women. For those with diabetes taking medication, medical supervision is advised.
- For athletes and really active people, the biggest challenge is having sufficient energy to support hard training. Intermittent fasting could impair the ability to train at high intensities unless athletes fasted on non-exercise days. In addition, ingestion of protein and carbohydrate consumed shortly after a weight training session enhances muscle protein synthesis and muscle growth. Resistance exercise coupled with food intake results in elevated insulin levels which in turn promotes protein synthesis. Fasting could impair the ability to repair and build muscle.
- The U.S. News and World Report for the Best Diets in 2018 rank The Fast Diet as #35 out of 40 plans evaluated. Not a very high score.
A study of longer duration (1 year) comparing IF to conventional calorie reduction found both achieved similar beneficial results. This infographic summarizes the study and the results.
The bottom line: If intermittent fasting helps you learn portion control and you don’t overcompensate on non-fasting days, and you don’t mind feeling hungry, give it a try. Be sure to spend your 500 or 600 calories wisely (no pumpkin spice lattes) by choosing lean protein (eggs, seafood, chicken, turkey, pork, or beef), plenty of low-calories vegetables, and drink lots of water.
Food & Fitness After 50 devotes a chapter to weight loss and maintenance with tips to help you achieve good health.