Intermittent fasting (IF) is a popular fat loss protocol. A few years ago, the mostly animal studies in the field of IF were very promising. More human research is now available, as well as more practical experience. How useful is IF actually and in particular for the natural bodybuilder?

We look at IF from three angles:

• health;
• fat loss;
• muscle growth.

WHAT IF MEANS

IF is a form of intermittent fasting and therefore not a diet as is often thought. IF does not determine what you can and cannot eat, but only when you can and cannot eat. People use IF to lose weight, improve their health and simplify their lifestyle.

Fasting is certainly nothing new; our body is designed for fasting. In prehistoric times we regularly had a period in which there was little or no food. Our fat reserves help the body through periods of scarcity.

IF METHODS

There are several ways you can fast. The three main methods are:

• the 16/8 method: you fast for 16 hours a day and eat the other 8 hours a day. This usually boils down to skipping breakfast, starting eating at 12:00 AM and not eating anything after 8:00 PM. This is the most popular form of IF.
• the  alternate day method: fast every other day;
• the 5/2 method: an eating pattern in which you eat your normal amount of calories 5 days a week and eat extremely little for 2 days (men 600 calories, women 500 calories per day). The big advantage of this method is that you ‘only’ eat little two days a week, so that your body is less inclined to go into saving mode (saving on NEAT).

IF AND HEALTH

IF is primarily intended for weight loss, but it also has the necessary health benefits attributed to it, which is why IF owes part of its popularity.

Healthline lists the most important health benefits, based on scientific research:

• Insulin resistance: IF can reduce insulin resistance, lower blood sugar and lower fasting insulin levels by 20-31%, which should protect against type 2 diabetes.
• Anti – inflammatory: IF reduces inflammation in the body through autophagy, the clearing of waste cells.
• Good for the heart: IF lowers the bad LDL cholesterol in your blood and ensures healthier blood pressure.
• Good for the brain: IF increases the brain hormone BDNF and can promote the growth of new nerve cells. IF may also protect against Alzheimer’s disease.
• Longer lifespan, at least based on rat research. Only in decades will we know whether this also applies to humans.

There are two important caveats to these purported health benefits.

In the first place, the health benefits are often partly or wholly due to the fat loss achieved, not specifically to fasting.

Second, there is still a lack of human research, as concluded in a 2015 review and noted by scientist and muscle growth specialist Brad Schoenfeld in a 2018 interview. In a more recent interview with Men’s Health, Schoenfeld says:

Diets will help you control your cholesterol, diabetes and other conditions simply because weight loss will help you control those conditions. The purpose of a diet or eating pattern is to facilitate weight loss.

Schoenfeld’s colleague Menno Henselmans is (even) more skeptical about the health benefits of IF. He bases this partly on a recent study in which 139 people were followed for a year during a calorie-restricted diet: one group with a continuous diet, the other group with IF according to the 16/8 method. The outcome: There were no significant differences between the groups in body composition change or metabolic risk factors, including insulin sensitivity, at 6 or 12 months.

Henselmans about this:

A new study now adds to the growing evidence that intermittent fasting has no meaningful health benefits independent of calorie restriction.

Schoenfeld and Henselmans receive acclaim from a new meta-analysis that concludes that fasting in itself provides no health benefit; it is the energy deficit that makes the difference:

Compared to continuous energy restriction, intermittent energy restriction showed no significant long-term differences in anthropometric, cardiometabolic, inflammatory, or appetite outcomes in the included studies.

In conclusion: more human long-term research is still needed to draw firm conclusions about IF and health.

IF AND FAT LOSS

Any health benefits are nice, but most people still fast because of the fat loss. After all, by not eating for part of the day, you create a calorie deficit throughout the day, provided you do not cross the line within the eating window. To this end, it is important that you use a calorie app, especially in the beginning .

The big question is whether IF is more effective for fat loss than a diet with continuous food intake. Based on two scientific reviews, from 2015 and 2016, this is not the case: IF is no better than regular weight loss, but no worse either.

From the latter we conclude that IF is a way of losing weight, a personal choice based on advantages and disadvantages.

ADVANTAGES

Perhaps the most important benefit of IF is psychological: you don’t have to worry about eating and drinking for an extended period of time. For some people that is more pleasant than being allowed to eat, but with major restrictions.

Brad Schoenfeld on this:

Fasting can help people control their appetite and food intake.

Another advantage is that you can eat whatever you want, provided you eat it within the eating window and provided the total energy balance is negative. As a bodybuilder, make sure that you meet your protein quota: eat about 2 grams of protein per kilogram of body weight per day. This is preferably spread evenly over three meals, because research shows that muscle protein synthesis is best stimulated in this way.

Furthermore, IF is easy for some to fit into the lifestyle. For example, if you don’t have breakfast, you already have a long fasting window, with the night’s rest on top of that. IF is therefore not so heavy.  This is also an advantage of IF that emerged from the aforementioned meta-analysis, as noted by Manno Hensemans:

IF can make energy restriction easier for people who aren’t naturally hungry in the mornings. Delaying the first meal of the day in this case usually leads to a decreased appetite during the day and a lower energy intake.

A tip for bodybuilders in the cut: Follow a 16/8 pattern, dropping the workout right between two large meals. Divide the proteins (~2 g/kg/d) evenly over the meals, so in portions of 20-40 grams. Do not train on an empty stomach, research shows.

Example:

16.00 meal 1
18.00-19.00 training
20.00 meal 2
23.00 meal 3 (protein powder)

CONS

However, IF is by no means suitable for everyone: it also has drawbacks.

In the first place, it takes a lot of perseverance to eat nothing at all for a long time. We mentioned that you should ideally use it in a lifestyle where you are already used to fasting for a longer period of time. But you’ll still get hungry. Anecdotal evidence shows that the longer you persist, the less the feeling of hunger will become.

Sometimes IF leads to compensatory behavior, with unhealthy food choices and excessive calorie intake during the eating window. The trick is to also control yourself during the eating window, which does not take away from the fact that you can finally enjoy eating again.

In addition, IF is difficult in social situations where you are expected to join the meal. Yet that only has to be a matter of moving your eating window for once.

There may also be fatigue, especially in the early stages of IF. This also means that you plan your training(s) during eating periods as much as possible.

IF is not suitable for everyone, especially not for: people with type 1 and 2 diabetes, pregnancy, underweight, for people under the age of 18 and people with a history of eating disorders.

CONCLUSION

All in all, we can say that IF can be a useful strategy for fat loss, but not for everyone. It just has to fit into your personality and lifestyle. Menno Henselmans:

If fasting is part of your lifestyle, it is a useful way to reduce your energy intake. If not, that’s fine too: you won’t miss any health gains or fat loss.

And finally:

IF is a useful diet aid for some, but certainly not a panacea for everyone.

IF AND MUSCLE GROWTH

So far, we’ve looked at benefits of IF specifically for health and fat loss. But what about muscle building, after all the main goal of the average gym-goer? Unfortunately, not much is known about it yet.

In principle, IF seems rather detrimental to muscle growth. As mentioned before, there is scientific consensus to eat 20-40 grams of protein every 3-4 hours. In this way, muscle protein synthesis is best stimulated. Within IF, your body is deprived of protein for a long time, which is not optimal for muscle growth.

What is positive is that fasting increases the growth hormone. More human growth hormone ultimately results in greater endurance and faster muscle recovery.

A meta-analysis of eight studies indicates that IF strategies lead to increased weight loss and fat loss (presumably by indirectly reducing calorie intake), without negatively affecting lean body mass. Coach and author Eric Texler concludes from this:

Time-restricted diets with an eight-hour feeding window are fine for supporting strength gains and hypertrophy, as long as the protein is high enough.

Within eight hours you will manage to consume at least three large portions of protein with enough time in between. So do not fast more than 16/8 and eat about 2 grams of protein per kilogram of body weight daily.

Another meta-study concludes that IF can more easily be at the expense of lean body mass than continuous diets.

Brad Schoenfeld is clear in his opinion of IF in relation to muscle growth and maintenance. In the interview with Men’s Health, he says:

Fasting does not benefit strength or muscle growth.

Our vision? If you’re bulking, IF probably doesn’t make much sense. In any case, if you enjoy fasting, don’t go more than 16/8 (otherwise you’ll be eating way too much in a short period of time) and plan your workout right in between two protein-rich meals. Training on an empty stomach is out of the question, we already said.

If you are cutting, in our experience IF can be a useful aid, especially with fat loss plateaus. Use 16/8 and plan your training exactly between two protein-rich meals. Preferably do not go more intensive than 16/8, so that you can continue to spread your proteins slightly.

It must be said, it probably just doesn’t matter for muscle growth whether you follow a continuous diet or use IF, as long as you eat enough protein and don’t train on an empty stomach.

CONCLUSION

Intermittent Fasting is a popular way to lose weight. This is partly because IF offers health benefits, but not all of which have been convincingly scientifically substantiated.

Furthermore, it is unlikely that you will lose fat faster with IF than with a ‘normal’ diet at the same number of calories. As is the other way around.

IF offers no specific benefits for muscle growth and strength gain. However, the 16/8 protol may be an aid in a heavy cut.

The most important thing in losing weight while maintaining muscle mass is:

• create a medium calorie deficit (20-25% of your maintenance level);
• eat enough protein (~2 g/kg/d);
• spread the proteins as much as possible throughout the day (in ‘shots’ of 20-40 g);
• do not train on an empty stomach.

FINALLY

The best diet or eating pattern is the one that you can stick to. Everyone has different preferences. If you can go without food for a longer period of time, give IF a chance and see if it suits you.