A few weeks ago, Coach Neal used Facebook to ask about fasting – who had done it, and what had been their experience. Fasting can come in many forms – eating between certain hours, fasting for 24 hour periods, fasting some days and limiting caloric intake other days, etc. Intermittent fasting has become a popular strategy to gain training adaptations and body composition goals. But is it right for you? Does it work better than other diet strategies?
Let’s start with some common regimens for intermittent fasting. The most popular fasting regimens tend to be one of the following:
Periodic Fasting – eat normally for 5 days of the week. For 2 non-consecutive days, reduce calorie intake, usually to 500-600 calories. Calories can be spread into smaller snacks or eaten as one meal after 24 hours of fasting (so, say you started at 7 pm the night before, you could eat 500-600 calories at 7 pm the next day).
Restricted Eating Period – eat normally, but only for a set window during the day. Most people using this plan eat during an 8 hour window starting around 10 am – 12 pm and lasting until 6 – 8 pm. This essentially equates to skipping breakfast, making lunch your first meal, and avoiding nighttime snacking.
Benefits of Fasting
Supporters of intermittent fasting have claimed a wide range of benefits from the practice, including UPDATE – NEW CLAIMS?
- Reduced inflammation
- Weight loss
- Faster metabolism
- Lower LDL and total cholesterol levels
- Improved blood glucose and insulin levels
- Protection against cardiovascular disease
After a brief review of PubMed (an extensive online research database), I came to the following conclusions:
1.Research demonstrates that intermittent fasting has beneficial effects on humans, including weight loss, body fat reduction, and improvement of some cardiovascular disease risk factors.
A 2015 systematic review (Horne et al 2015) found positive effects on weight loss and other cardiovascular risk factors (like cholesterol) in 3 of the 5 studies. And in 2 of the studies – long term observational studies – fasting was associated with a reduced risk of coronary artery disease.
Another 2015 review (Tinsley et al 2015) examined studies in varying intermittent fasting plans – alternate day fasting (alternating fasting and normal days in which the fasting day is about 500 calories), whole day fasting (fasting 12-24 hours), and time restricted eating. The results showed that alternate and whole day fasting lasting 3-12 weeks reduced weight (3-7% and 3-9% respectively) and body fat and had positive effects on blood lipid levels. Data on time restricted eating was too limited to draw conclusions.
Barnosky et al 2014 reviewed data comparing calorie restriction and intermittent fasting – including time restricted eating and alternate day fasting – among overweight and obese adults, and found that while calorie restriction produced more weight loss, the two regimens produced similar reductions in fat mass, fasting insulin, and insulin resistance.
2.Intermittent fasting may not be all that helpful for serious athletes.
A good portion of the human studies on intermittent fasting in athletes were conducted among people observing Ramadan, and many were geared toward limiting the negative impacts of the fast versus assessing its potential benefits. This makes sense, given that Ramadan fasting is unlike other types of intermittent fasting, as it requires observers to fast every day for one month from sunrise to sunset. How long these fasts are depends on the season in which Ramadan occurs.
Research indicates that the effects of Ramadan fasting are small if the athlete maintains energy and fluid intake during eating times, maintains a normal training schedule, and gets 8 hours of sleep. A 2016 study of karate athletes indicated Ramadan may not negatively impact reaction time and neuromuscular performance (Zarrouk et al 2016). However some studies have also shown that Ramadan fasting lead to decreased power and increased muscle fatigue in football players, decreased performance among middle distance runners, loss of sleep, and increase in subjective fatigue. In addition, most studies on Ramadan have been conducted when it took place during winter months – with shorter days and milder weather – and more research is needed for times when Ramadan falls in the summer.
My Takeaway? Cutting out extra calories is a well-recognized strategy for losing weight and improving health overall. IF is just as good a strategy as a “normal” lower calorie diet for cutting back on calories. Given the lack of data available, I wouldn’t recommend it as a strategy to improve athletic performance.
A few things to consider when fasting
- Avoid Blanket Prescriptions. Most alternate day fasts prescribe 500 calories for women and 600 for men on fasting day. But what about differences in energy needs among different people? If I’m a small woman doing little exercise, 500 calories might be about 1/3 of my usual daily needs. But if I’m a larger man doing high intensity interval training (like CrossFit) 5 times a week, 600 calories might be less than ¼ of my usual daily needs. Some presrciptions call for 75% energy reduction, which makes more sense.
- Consider if it really makes sense for you. One of the frequent arguments in favor of IF is that we evolved this way – “the caveman” often fasted because he didn’t know when his next meal was coming. And of course we all know the caveman had a six pack and no heart disease, right? But the simple fact that our ancestors did something out of necessity does not mean it is good for us. Our ancestors also splinted broken bones with twigs because they didn’t have plaster casts and died from what would today be a fairly minor wound because they didn’t have antibiotics.
- Eat healthfully when you’re not fasting. Fasting can be a beneficial strategy. But it’s only helpful if the free eating days/times also contain nutritious choices – lean protein, vegetables, fruits, healthy fats from nuts, fatty fish, and avocado, whole grains, etc. Fasting for 18 hours and then eating fast food and Snickers bars is not an ideal strategy.
So, Should You Try Fasting?
The question isn’t really whether you SHOULD fast, but whether you COULD fast. I recommend a stable diet consisting of quality foods, with intake based on hunger cues. However, the what, why, when, and how of eating is different for everyone. So if you wanted to try fasting as a way to lower calorie intake, then I think it is a good strategy worth trying.
When I consider recommending intermittent fasting, it would be to help with a behavioral issue. For example, if someone had lost their ability to detect hunger cues. It’s easy in our American culture of food availability and glorification of “busy” to stop eating for hunger and start eating for a bunch of other reasons. You eat breakfast because it’s 8 am and you need to leave for work. You eat lunch because your coworkers are all going to that new Mexican place at noon. You eat a snack at 4 because you’re bored. And so on. In a case like that, a week or two of intermittent fasting can help reset your awareness of hunger and recognize the difference between actual hunger and other types of hunger.
A few tips if you choose to fast:
- Make sure your “normal” diet is on track. Limited eating periods and non-fast days are NOT an excuse to eat whatever whenever. IF only works as a method for calorie restriction if you maintain healthy, moderate eating habits during non-fasting periods. And alternating fasting with poor eating habits might be a good way to end up lacking important vitamins and minerals.
- Plan ahead. If you decide to do your long run or 2½ hour Olympic lifting class on a fast day, you might pay for it in the form of poor performance and fatigue. Especially when you’re starting out, plan fast days to coincide with lighter training days.
- Listen to your body. Don’t stick to IF because it’s supposed to have all these benefits if it doesn’t feel right for you. If you’re tired all the time, losing sleep, and not seeing results, it’s time to try a new strategy.