Find out what scientific research says about what to eat in intermittent fasting.
There are diets that tell you what to eat, others that dictate what not to eat, and then there’s intermittent fasting, which (perhaps) doesn’t make you eat at all.
What is it and how does it work? Basically, this eating strategy structures your days into periods when you can eat and others when you fast.
Like any other proposal, it has its pros and cons, in terms of adherence, effectiveness, effect on muscle mass – certainly an extensive topic if you are an athlete, work out in the gym, or do bodybuilding.
What Is Intermittent Fasting?
Intermittent fasting (IF), or intermittent fasting, is one of the most discussed diets in recent years, especially in the fitness environment.
On the one hand, supporters praise its benefits regarding weight loss, the positive effects on cardiovascular risks, and lengthening life, on the other hand, detractors consider it a simple fashion destined to end up in oblivion in a short time like many other diets.
In fact, in recent decades the number of so-called Fad diets has grown exponentially, a term that can be translated as “ trendy diets ” or “diets of the moment”.
The Fad Diet is a diet that enjoys temporary success and that promises sensational results in a short time, such as weight loss, increase in muscle mass, and improvement in the quality of life in general. But these promises are almost never kept, at least in the long term.
Given the widespread use of such diets, the question often arises whether even intermittent fasting can only be considered a fad or if it really has real health benefits.
Questions that in recent years have also been posed by numerous researchers who have intensified their studies on this food method.
How Does Intermittent Fasting Work?
Although there are different versions of intermittent fasting in the scientific literature, there are 3 main forms studied which are the ones we will consider in this article, namely: ADF(Alternative-day fasting), WDF(Whole-day fasting), and TRF(Time-restricted feeding).
This subdivision is simply done for the different fasting time windows.
1. Intermittent Fasting: Alternative-Day Fasting
The ADF is the intermittent mode fasting most studied in the literature and consists of alternating days of complete fasting, or at most of the consumption of a meal only 400-500 kcal, to days of free food intake.
The calories not introduced in the days of fasting are hardly recovered in the days you eat thus creating a caloric deficit that is responsible for weight loss.
Some studies have shown that this fasting mode reduces total cholesterol, LDL cholesterol, and triglycerides.
Some studies have also shown greater efficacy in maintaining muscle mass compared to simple calorie restriction even if the tools used to detect the data collected, such as the BIA, are not entirely reliable.
2. Intermittent Fasting: Whole-Day Fasting
The WDF is a type of fasting that involves one or two days of complete fasting during the week and a normal caloric diet in the remaining days so as to achieve a weekly caloric deficit.
The real effectiveness of this strategy is not yet clear in the literature as some studies have shown a greater loss of fat mass compared to the classic calorie restriction, while others have not shown any advantage.
This is because studies are often conducted with a different fasting window.
3. Intermittent Fasting: Time-Restricted Feeding
The TRF protocol, on the other hand, provides for the alternation of phases of fasting to phases of nourishment over the course of 24 hours.
Although the most studied model in the literature is Ramadan, the most used model remains the 16/8 which provides for the alternation of 16 hours of fasting with 8 hours of nutrition.
Another well-known model of the TRF type is the Warrior Diet made famous by Ori Hofmekler’s book of the same name in which the feeding window is reduced to just 4 hours in the evening.
What To Eat In Intermittent Fasting?
Intermittent fasting is defined more as a food strategy than a diet precisely because it does not give references on what to eat, what not, which macronutrient to give more space to, what to limit, etc.
It only gives a time reference, more or less wide windows depending on the protocol chosen in which to fast and others in which to consume the meal.
From this it follows that you can basically eat what you want, always considering that a healthy and balanced diet is to be followed.
A point on which you can pay more attention is the case in which the hours in which to eat are reserved for the late afternoon/evening, before going to sleep.
In this case, for a more peaceful sleep, it is good to let at least 2- 3 hours (depending on the abundance of the meal) before going to bed. Thus, time is left for digestion.
For a healthy and balanced diet, even with the strategy of fasting, it will be necessary to pay attention to the quantity and quality of food just as it is possible to lose weight with intermittent fasting, in the same way, you can also gain weight if you eat too much in that period of time than what you need!
Intermittent Fasting In The Gym And Bodybuilding
If the main concern of approaching intermittent fasting for the first time is the loss of muscle mass – especially among athletes – you can rest assured that intermittent fasting is also effective in maintaining muscle tissue in conditions of calorie deficit.
A study even demonstrated a greater ability of ADF to retain a greater amount of muscle mass than continuous calorie restriction even if the tools used (BIA) are not entirely reliable.
One of the largest meal frequency reviews conducted by researchers Aragon and Schoenfeld in 2015 showed that meal frequency does not affect body composition.
It hardly makes any difference whether you decide to eat 2, 3, or 6 meals a day.
It is the total calories consumed over the weeks and months that make the difference; this is true at least in sedentary subjects.
Unfortunately, the scientific literature is devoid of research that correlates intermittent fasting, in all its modalities with the growth of muscle mass.
Studies that include weight training programs while fasting are also nearly absent.
One of the few studies was conducted recently (2016) by an Italian research group headed by Antonio Paoli and Grant Tinsley.
In the research, conducted for 8 weeks, a slight increase in muscle mass was noted both in the group that had followed the intermittent fasting and in the group that had followed a classic normal caloric diet.
However, there are theories, even if not completely confirmed in the scientific field, which state that it would be better to consume about 3-4 meals a day spaced about 5-6 hours to maximize hypertrophic gains (the average duration of the anabolic effect of a meal).
According to these theories, fasting would therefore not be ideal for optimizing muscle growth even if this does not mean that improvements in muscle mass cannot be obtained in any case.
The advice is therefore to use intermittent fasting during the maintenance and weight loss periods and to prefer a division of meals throughout the day in the periods in which you want to obtain an increase in muscle mass.
How Much Is Lost With Intermittent Fasting?
Promoters of intermittent fasting often refer to acute hormonal changes to demonstrate the efficacy of fasting in promoting weight loss.
During fasting, there is in fact an increase in the concentration of catecholamines, glucagon, growth hormone, a lowering of insulin levels, and greater lipolysis.
However, these hormonal changes have nothing to do with long-term weight loss.
The reason why intermittent fasting can help in weight loss is simply through the reduction of calorie consumption favored by the reduced time window in which it would be allowed to consume food.
The fact that intermittent fasting does not give any additional benefit on fat loss over many other calorie restriction diets is well established in the literature.
For example, in 2015 Seimon and colleagues published an extensive review that collects about 40 studies on the correlation between intermittent fasting and weight loss.
Among these 40 studies, 12 in particular directly compare intermittent fasting with continuous calorie restriction. The researchers found no difference in fat loss between the two diets.
Fasting is not superior in improving glycemic control and insulin sensitivity, nor in improving the hormonal picture including the levels of cortisol, thyroid hormones, or sex hormones (indeed in this case it would seem there is a greater decrease of testosterone).
However, a greater effect in hunger control was noted, probably due to the greater production of ketones.
Intermittent fasting does not seem to have any efficacy in countering the metabolic adaptations that tend to occur during weight loss compared to diets with continuous calorie loss.
These results were then confirmed by another meta-analysis published the following year, in 2016, by Headland and colleagues.
Even if intermittent fasting, in all its variants, has never been superior to the classic calorie restriction, it is still an effective strategy for weight loss, especially when it can help in maintaining dietary compliance and calorie deficit over the course of weeks.
Intermittent Fasting For Women
Studies on intermittent fasting conducted on women have also not shown any superiority in weight loss, although it has nevertheless proved to be an effective alternative strategy.
However, physiology says that men and women respond differently to calorie restriction due to the different concentrations of sex hormones.
Women, in a condition of continuous caloric deficit, can develop pathological conditions such as amenorrhea ( absence of menstrual cycle ), or dysmenorrhea ( menstrual cycle disorder ) especially when the deficit is very marked.
The minimum threshold of calories recommended avoiding alterations in the menstrual cycle is equal to 30 kcal/lbs / LBM or just under 1500 kcal for a woman of about 132 lbs (in reality there are many girls who do not lose weight with these calories).
A calorie consumption below this threshold can lead to the appearance of menstrual disorders such as alteration of the luteal phase, oligomenorrhea (17%), and amenorrhea (22%).
These alterations occur mainly when calorie restriction is maintained for a long time.
The use of intermittent fasting, especially in the ADF mode, which alternates days of complete fasting with days of ad libitum caloric intake could be a good strategy to avoid hormonal alterations of various types although as far as I know there are no studies that can confirm this.
For this purpose, especially for women who practice physical activity in the gym, a fasting protocol known as EOD Refeed ( Every other day refeed ) was devised by Lyle Mcdonald.
It consists of alternating days in which they take only proteins on rest days to days in which you follow a normal-calorie or slightly high-calorie diet on training days.
In this way, not only is a more or less evident weekly deficit maintained but it is possible to avoid hormonal alterations and obtain a body recomposition effect when the calories in the refeed days are high enough.
Intermittent Fasting Negative Effects
Among the negative effects of fasting, reference is often made to the possible appearance of eating disorders.
In 2004, the Canadian Pediatric Society defined chronic diets, fad diets, fasting, and skipping meals as unhealthy eating strategies in reference to diets in adolescents.
The DSM-IV, or the diagnostic and statistical manual of mental disorders, also includes fasting among the “recurrent and inappropriate compensatory behaviors to prevent weight gain”.
Can intermittent fasting, since it is an alternative form of fasting, actually lead to eating disorders?
This is the question posed by researchers from the Department of Kinesiology and Nutrition at the University of Illinois at Chicago.
The group, led by Kristin Hoddy, wanted to examine whether Alternative-day fasting (ADF) could contribute to altering the perception of body image and manifesting symptoms of eating disorders.
The study was conducted for 8 weeks on 59 obese subjects who were asked to consume 25% of their daily caloric needs on “fasting” days and eat ad libitum on the remaining days.
This is the most important study – among other things also the only one – that has evaluated the safety of intermittent fasting with regard to eating disorders.
From the results of the research, it emerged that intermittent fasting in the ADF form does not increase cases of depression, binge eating, food abuse, and nervous hunger, the fear of gaining weight or consuming foods considered unhealthy but also improves the perception of one’s body image.
However, attention must be paid to extending these results to other types of subjects. Eating disorders are common in teenagers.
It is, therefore, necessary to be very cautious in believing that children can have the same positive effects of intermittent fasting as adults, “says Alan Aragon.
It is still unknown whether these results may also concern other fasting modalities such as the 16/8 or the Warrior Diet and what are the effects of intermittent fasting on people who have already suffered from eating disorders.
In any case, with the data available today, no negative effects of IF on DCA have ever been demonstrated.
Conclusion On Intermittent Fasting
Intermittent fasting is not a miracle diet as the media sometimes tend to pass but it is simply a diet like many others.
However, it remains a good strategy to adopt to facilitate the achievement of the weekly calorie deficit which is the only factor that really contributes to weight loss.