Should You Recommend Intermittent Fasting to Your Personal Training Clients?


Seeing client after client struggling to reach their ‘weight loss goals’ can be a frustrating feat for many personal trainers. So much so that it’s forced me to question the very foundation of the weight loss and fitness industry all together. While it might be tempting to hand over a quick fix to your training clients who really want to “see” results, I think it’s important to really look past the smoke-and-mirrors and see beyond the extreme claims that so many diet and lifestyle fads recommend. The one that seems to be on everyone’s minds lately? Intermittent Fasting (IF).

At first glance, Intermittent Fasting looks innocent enough. Unlike many fad diets that focus on restricting calories or specific food groups, IF has pretty loose guidelines on the amount and type of food you can eat. Instead, IF requires you to manipulate when you eat rather than what you eat and is defined by periods of voluntary abstinence from food or drink, aka fasting. While IF recommendations are inconsistent at best, the typical recommended pattern is a 16 hour fast, followed by an 8 hour eating window. For example, you would be required to stop eating at 3pm one afternoon, and you wouldn’t eat again until around 7am the next day.

IF claims to reduce body fat, increase lean muscle mass, increase insulin sensitivity, aid in longevity, and even reduce the risk of cancer. Sounds amazing, right? Don’t get too excited. Nearly all of the research done on Intermittent Fasting has been performed on mice, not humans. Although arguably comparable, humans have extremely complex metabolisms and functions that simply cannot be replicated in mice. Additionally, most of the research performed in the service of observing the benefits of IF have only been done short-term, and provide no context of the long-term effects of fasting.  

However, there is one notable experiment that can provide further insight into the harmful effects of the IF protocol: The Minnesota Starvation Experiment. Done in 1944, this experiment is a prime example of why intermittent fasting is unreasonable and detrimental to overall health. This study follows a group of young men where they were purposely, but controllably starved in order to understand the most effective way to provide post-war rehabilitation through refeeding after a long period of deprivation. A participant of the study stated, "we were starving under the best possible medical conditions. And most of all, we knew the exact day on which our torture was going to end." However, if you’ve followed my work before, you know that the body does not know the difference between an intentional fast, and a life threatening fast. We have hardwired survival instincts that don't know the difference between a 16 hour fast and a famine.

The most surprising findings from this study are the behavioral effects of fasting. Deprivation cause these men to become hyper-fixated on food, binge when they were in the presence of food, and increased overall anxiety around food. When the experiment was over, the participants reported an inability to distinguish between the constant gnawing of hunger and normal appetite. Needless to say, if there were any physiological benefits to their fasting they didn’t last after the experiment was over. Plus, their mental, emotional, and social health was diminished in the process.

This type of diet specifically raises concern for bingeing, since the “feeding window” is structured to only a certain number of hours, requiring the client to only eat 1-2 meals consisting of their entire day’s worth of calories. Not only does this cause a person to be hyper-fixated on their food, it causes them to be less in-tune with their body’s natural hunger and fullness cues, or worse, causes them to ignore those cues altogether.

In my recent conversation with Registered Dietitian and Certified Strength and Conditioning Coach, Matt Stranberg, he outlined some sound, evidence based nutrition recommendations you can provide to your clients, without going to the extreme of daily fasting. While these recommendations were not included in the video linked above, I am going to outline them here for your reference.

Energy & Hydration Adequacy
While it might be tempting to recommend clients restrict their caloric intake in an effort to lose weight, it’s also the fastest way to reduce the body’s response to training. Adequate energy (calorie) intake, and adequate hydration are the first essential component of a balanced diet.

Consistent Feeding
While this advice contradicts intermittent fasting, eating every 3-5 hours (about 4 times per day) is essential to balancing blood sugar levels, and helping your clients stay in tuned with their body’s natural hunger and fullness cues. Additionally carbohydrate stores (your body’s main source of energy) will deplete every 3-5 hours, so fueling and refueling before and after a workout can ensure adequate energy stores throughout the day.

The three main macronutrients are carbohydrates, protein, and fat. This means that all three of these macronutrients are essential to maintaining a healthy diet, and no one is more important or less important than the other. Carbohydrates and fat provide your body with much needed fuel for daily life and for training, while protein provides amino acids to maintain muscle and bone.

Micronutrients are compounds like vitamins and minerals, and while they are present in all foods, they are most concentrated in fruits and vegetables. While fruits and vegetables are a key component to a healthy diet, they are not the only healthy component. Our body will process all of the nutrients found in these foods, when we are eating adequate amounts of energy and macronutrients, and being mindful of our fluid intake. Additionally, many of these compounds can help mitigate inflammation, a natural process the body undertakes when training.

While I would argue that IF is not suitable for most clients, it is definitely contraindicated for those with a history of, or currently struggling with an eating disorder. Make sure to check out my Intro to Eating Disorder article, and my interview with Matt Stranberg for more guidance on how to work with this population.

What are your questions or thoughts on Intermittent Fasting? Let me know in the comments below!