Intermittent fasting (IF for short) is at the top of the list of the most popular diets of the past decade with the keto diet. Which is a bit ironic considering that fasting has been practiced for centuries – albeit primarily for religious and spiritual purposes – compared to the potential health and weight loss benefits that have made its general appeal in recent years.
Despite IF's vast experience and growing scientific research confirming its safety and effectiveness, many questions remain unanswered, many of which are answered below by one of the most knowledgeable nutritionists in the US military.
Susan Lopez is a tactical performance dieter who specializes in working with some of the bravest Americans – from military athletes to firefighters, police officers, and first responders. Lopez is a military veteran and special operations spouse whose unique experience and knowledge helps elite war fighters and community heroes stay fit and healthy. She is also the team dietitian for Bravo Sierra.
What goals and people is intermittent fasting best for? And what specific IF protocols are best suited to achieve these goals?
The intent of any type of IF is to stimulate weight loss by reducing or restricting calories, which has been linked to improved hormone levels and other biomarkers. IF should not be viewed as a performance diet, but as a strategy for optimizing health and weight loss. Individuals with physically demanding jobs or who consider themselves athletes may need to consider other strategies to maintain performance levels.
Popular IF strategies include fasting for 18 hours, including sleeping, and eating for the remaining six hours of the day (also known as 18: 6). Another method is to eat normally five days a week and then consume about 500 total calories (also known as 5: 2) on each of the other two days. A third popular method is to eat normally six days a week, followed by a 24-hour fast.
If an athlete chooses to use IF, it is recommended that they carefully consider training plans or sports competitions. And just like any other low-calorie diet, a specific start and end date with maintenance phases or “diet breaks” should be set so that the metabolism works efficiently. People with a medical condition such as diabetes, cardiovascular disease, or other metabolic disorders should not use intermittent fasting and should consult their doctor before undertaking any nutritional program.
Would you recommend any of the three popular IF health and weight loss strategies to the others? Or is it more about which of the three best suits your lifestyle?
Assuming the calorie restriction is the same across styles, any style can work that suits the person's schedule and personal preference. In most cases, the 24-hour fast is the easiest to manage because it really doesn't require any thought other than not to eat for a whole day a week. Many people find that it is easier to feel uncomfortable one day than to limit yourself on a daily basis.
You mention people with physically demanding jobs and athletes as the ones who may not want to do IF. What about people who don't have both, but are seriously interested in fitness and could, to some extent, be considered athletes?
Calories should be available when physical activity is at its peak to compensate for the higher energy needs at these times. IF can also be used on days of rest or relaxation so as not to limit the availability of energy on training days. Energy availability refers to the energy that is left for metabolic functions outside of physical training. Even for sedentary, recreational, fitness, or aesthetic individuals, IF should be a targeted and planned activity or cycle.
When you say "Exercise Plan Considerations" to athletes doing IF, are you specifically talking about making sure you are getting proper nutrition before and after your exercise? Do you discourage sober training?
For the most part, exercising on an empty stomach has no confirmed benefits, especially in terms of weight loss that simple calorie restriction cannot achieve. I don't usually encourage it as it could negatively affect hormone levels.
What kind of “diet breaks” would you generally recommend?
The steeper the calorie deficit, the shorter a "diet cycle" should be and the longer a diet break may need to be. Research has shown that low energy intake and availability over long periods of time has negative effects on resting metabolism. Sex and endocrine hormone levels such as thyroid; as well as mood, muscle retention, and bone health.
I usually don't let an athlete take a hard "cut" (more than 400 to 500 calories) at any one time for more than five to six weeks while dieting. Then I put them in for a week or two to maintain the calories before I move on to another cutting phase or training cycle. Lower deficits (around 300 calories or less) can be used for longer periods of time (i.e., 12 weeks) for someone looking to stay highly active or experience less degradation during a cut.