Krista Varady PhD is an Associate Professor of Kinesiology and Nutrition at the University of Chicago-Illinois. Her research is described as follows: “The long-term goal of my research program is to test the ability of novel dietary restriction strategies to facilitate weight loss and decrease cardiovascular risk in obese populations. At present, there are many dietary approaches to weight loss. However, if one diet were clearly superior in helping obese individuals lose weight, than only one dietary intervention would be needed. In reality there are a number of obese individuals who have tried each of these diets, but have failed to adhere to them and observe weight loss. As such, new dietary interventions need to be tested to provide obese individuals with options for weight loss. The most common dietary restriction protocol implemented is daily calorie restriction (CR), which involves reducing energy intake by 15 to 40% of needs daily. Another dietary restriction regimen employed, although far less commonly, is alternate day fasting (ADF). ADF regimens include a “feed day” where food is consumed ad-libitum over 24-h, alternated with a “fast day”, where food intake is partially or completely reduced for 24-h. ADF regimens were created to increase adherence to dietary restriction protocols since these diets only require energy restriction every other day, rather than every day, as with CR.” (reference: http://www.ahs.uic.edu/facultyresearch/profiles/name,2052,en.html)
What’s the difference between alternate day fasting and following a lower kcal diet? Are the effects on body comp/weight different?
Dr Varady: ADF involves a “fast day” where a person consumes 25% of their energy needs either as a lunch or dinner, alternated with a “feast day” where a person is permitted to consume food ad libitum. On the other hand, daily calorie restriction (CR) involves consuming 75% of energy needs every day. We are currently running a year-long NIH-funded study to compare the effects of ADF to CR. So far, our results show that weight loss is similar (1-3 lb/week) between diets, however, ADF results in more maintenance of lean mass than CR. More specifically, with CR, a person loses ~25% of weight as lean mass and 75% as fat. With ADF, a person only loses 10% of weight as lean mass, and 90% as fat.
What are the health effects of intermittent fasting (IF)?
Dr Varady: ADF has been shown to decrease LDL cholesterol, triglycerides, fasting glucose levels, insulin levels, and insulin resistance. These effects are seen approximately 4-8 weeks after starting the diet.
Do you think IF has a role vis a vis athletes?
Dr Varady: We have yet to do a study in athletes. However, I think athletes could benefit from the lean mass retention seen with ADF. Retaining lean mass is also beneficial for maintaining resting metabolic rate.
Is there a sex difference regarding the effects of IF?
Dr Varady: Our studies have not been powered to detect sex differences, unfortunately (our sample usually consists of 80-90% females).
If someone were to do an IF or alternate day fast, is there a certain macronutrient ratio that you’d recommend?
Dr Varady: In a recent study, we show that a person can consume a high fat diet (45% kcal as fat) during ADF, and see the same weight loss and cholesterol-lowering benefits as observed with a low fat diet (25% kcal as fat) during ADF. Whether or not consuming a high protein diet yields the same effects has yet to be determined, however. We plan to run this study in the next year or so.