Is intermittent fasting good for your health?

Cláudia Salgado


Intermittent fasting has been a controversial issue in the field of sports and health lately. However, this popularity may not be related to its actual benefits and results on a physiologic and metabolic level. This is a nutritional pattern in which food intake is limited to a short, very specific period of time.

It should not be called a diet because it doesn't tell you what you should and should not eat, but rather the moment of the day in which food should be ingested. In fact, intermittent fasting can be included in all kinds of diet and is quite common in low-carb and paleo diets.

"It should be noted that intermittent fasting has been studied mainly as a strategy to lose weight in overweight or obese individuals." If that's your situation, check out this cardio training plan for weight loss: Beginners and experienced athletes.

Before going into further detail, it's important to make something clear: whatever the approach you choose, you should understand its impact on your health and if it's a sustainable healthy lifestyle.

Different methods of intermittent fasting

Once intermittent fasting became more common, a number of somewhat different methods arose as well.

Time restriction (or 16:8 method)

In this case, there is a time-restricted period in which individuals can't eat, and meals should be taken during the rest of the day. The most common method is based on a 16-hour fast and an 8-hour eating period (e.g. eating is allowed from noon to 8 pm).

Alternate-Day Fasting (or Eat-Stop-Eat)

Fast from dinner to dinner once or twice a week.

Whole-Day Fasting

This method specifies food ratios, such as the 5:2 diet, according to which individuals restrict calorie intake to 25% of their daily calorie needs.

Is intermittent fasting good or bad for your health?

Some people say that, even though eating during a given period of time is forbidden, after that you can eat anything, whatever it may be. This can lead to typical "binge eating" behaviours, i.e. compulsive overeating. On the other hand, there are more reasonable methods that include a balanced diet on most days, and where fasting should happen sporadically, for an extended period of time, seldom cheating.

Intermittent fasting has been widely publicised through social and other media, and a great deal of information has been made available, not always from the most reliable sources. The impact and benefits of this practice for your health are still unclear. A problem associated with this practice is the lack of scientific proof from good quality trials on intermittent fasting in humans. The results observed in animal trials can in no way be used for humans, nor can they serve as a basis to create a new diet plan. A

s human beings, the only scientific evidence that matters is the one derived from human trials, not the ones done on lab animals. Very few human trials have been carried out, and all of them have many restrictions, such as diet type, sample size, or fasting and trial duration. It's therefore difficult to tell whether the benefits of intermittent fasting are sustainable or not, mainly when it comes to one's long-term health condition.

In very general terms, the benefits of intermittent fasting include:

  • Weight loss and/or fat mass loss
  • Improved insulin sensitivity
  • Inflammation reduction
  • Less oxidative stress

Trials show different results in obese and normal-weight individuals

Overweight/Obese individuals

It should be noted that intermittent fasting has been studied mainly as a strategy to lose weight in overweight or obese individuals. Under these conditions, trials showed that intermittent fasting is effective in weight and visceral fat mass reduction. Yet, similar results have been achieved with energy-restricted diets. (1) Apart from similar effects on a weight loss level, intermittent fasting and calorie restriction showed comparable reductions in C-reactive protein (an inflammation marker), total and LDL cholesterol, triglycerides and blood pressure. (2, 3)

A trial update (4) refers that there are no differences between intermittent fasting and an energy-restricted diet in terms of weight loss. Therefore, we can't know for sure if the benefits associated with intermittent fasting are related to this food pattern or to having lost weight. This update also says that what little evidence there is supports the idea that daily calorie restriction and intermittent fasting deliver the same results in controlling type 2 diabetes mellitus, cardiovascular markers (cholesterol and triglycerides) and in reducing inflammatory parameters.

All this to say that, in terms of metabolism, the benefits of intermittent fasting depend entirely of the calorie restriction it causes. Since all available trials are short-term (1 day to 12 weeks), it's risky to say that intermittent fasting has a great impact on cardiovascular diseases, cancer, diabetes and Alzheimer's.

Thin or normal-weight individuals

In trials whose sample included thin or normal-weight individuals, intermittent fasting did not seem to have many benefits, and it doesn't counteract the negative effects of a sedentary lifestyle. (1, 6). It should be highlighted that intermittent fasting has not been tested in children, teenagers, the elderly or individuals in a process of hypertrophy, so the effects that can be observed in these groups are not clear. From a psychological point of view, there have been some negative implications, such as irritability, mood swings, and a decrease in energy and concentration. (1) These can be the result of decreased serotonin (also known as the well-being hormone) production.

Main conclusions: be wary of signs of eating disorders and focus on your goal

Although studies have shown you can lose weight with intermittent fasting, some individuals gained weight due to overeating on the days they didn't fast. This practice can lead to eating disorder behaviours, and some people may develop an unhealthy relationship with food. Things to keep in mind:

1) Lack of scientific studies

Even though I'm not exactly against intermittent fasting, additional studies are necessary to judge its effects on metabolism.

2) Losing weight is not its only goal

There are no fixed rules regarding weight loss – intermittent fasting is just one more way to lose weight. It's a matter of personal choice!

3) Be careful with calorie restriction

Calorie restriction is mandatory to lose weight, i.e., you should eat less than you spend. Still, not all strategies are good when it comes to losing weight and preserving muscle mass at the same time.

4) See a nutritionist before you start

Doing intermittent fasting is fine, as long as you do it wisely, while being monitored by a qualified professional.

5) It can be beneficial depending on how you deal with food

Intermittent fasting is a viable option for people who don't wake up feeling hungry or for those who are not organised and are not in the mode to snack throughout the day. Intermittent fasting is probably the best way for them to deal with food.

6) Above all, be cautious and sensible

You should be very cautious because intermittent fasting lacks scientific evidence. For you, this may seem to be the best way to meet your goals, but it may not be so effective for others. When it comes to nutrition, we should bear in mind the individual needs of each person.

What to eat after fasting

The priority for those doing intermittent fasting (and everyone else) should be the nutritional quality of the food. Doing intermittent fasting is not a free pass to eat whatever you want. After an extended fasting period, choose your first meal wisely: it should be high in protein and fat and low in carbohydrates. If carbs are essential to your diet, choose food with a low glycaemic value, such as fruits.

Remember that consistency is the key to achieving your health and body composition goals.


  1. Seimon, R.V, et al.,, (2015). Do Intermittent Diets Provide Physiological Benefics Over Continuous Diets for Weight Loss? A Systematic Review of Clinical Trial. Molecular and Cellular Endrocrinology.
  2. Harvie M N et al., (2011). The effects of intermitent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International Journal of Obesity 35, 714-727.
  3. Headland M et al. (2016). Weight loss outcomes: A systematic Review and Meta-Analysis of Intermittent Energy Restriction Trials Lasting a Minimum of 6 Months. Nutrients 8(6):354.
  4. Mattson MP et al. (2017).Impact of Intermittent Fasting on health and disease processes. Ageing Research Reviews. 39:46-58.
  5. Patterson RE, Sears DD.(2017). Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition. 37:371-393.
  6. Harder-Lauridsen Nm et al. (2017). Ramadan Model of Intermittent fasting for 28 d had no major effect on body composition, glucose metabolismo or gognitive functions in healthy lean men. Nutrition 37:92-103.
Cláudia Salgado


Cláudia Salgado has a degree in Nutritional Sciences from the School of Biotechnology of the Universidade Católica Portuguesa and is certified in Sports Nutrition by WellX Proschool and Nutriscience Education and Counseling. She practises cross training and has a passion for nutrition, being fascinated by the impact food and lifestyle have in improving one's health condition.


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