An expert explains why intermittent fasting might not be good for you

Janessa Villamera
Thinking about trying intermittent fasting? Maybe you should think again.

MANILA, Philippines – It’s the word of mouth of the people around you, it’s all over the Internet… but what is intermittent fasting or IF all about?

Generally, IF means you only have a particular time window to eat. The rest of the day, you have to fast. One “type” of intermittent fasting entails an 8-hour window to eat. The remaining 16 hours of the day, you have to fast.

Sounds simple? Not really. 

Rappler talks to Juvy Martillos-Sy, Philippine Registered Nutritionist Dietician (RND) and US Registered Dietician Nutritionist (RDN), Chief Nutritionist Dietician of Asian Hospital and Medical Center, to explain that while IF is the fad right now, it’s still not a good weight loss option.  

“The public is being influenced that IF is an easy strategy for weight loss. We are hungry for ways to decrease our weight. But the public doesn’t have a background on how it works, so we appreciate if you approach a medical practitioner for scientific studies about it,” said Martillos-Sy.

(Editor’s Note: We’ve condensed some of her responses and translated some of the quotes from Filipino to English. We have also corrected some translations from an earlier version of this story.)

What is intermittent fasting and its different types?

Intermittent fasting, you’re going to check the word itself… it’s not a diet. It focuses on the eating schedule that we implement based on our eating lifestyle. As of now, based on its popularity, it’s being applied as a weight loss program.

If you talk about intermittent fasting as a diet, we check in different diets but it falls as a fad diet, if you’re going to use it for weight loss. It’s popular as a weight loss program.

We have an application… if you talk about the [Islamic] world, they also fast. [But] if you’re going to focus the discussion on weight loss, weight change, change in metabolism, it’s a case-to-case basis. The different types of intermittent fasting that we have encountered [include one] based on the number of days, 5:2. For 5 days, the individual can eat ad libitum, you can eat anything based on your ability, the volume you can consume, that’s how much you can eat. And then the 2 days, an individual eats 25% of the usual energy needs.

For example, I normally eat 2000 calories daily, so 25% of 2000 calories is only what you’re allowed for 2 days.

The other type, you really fast. They don’t eat anything. Another description for intermittent fasting is scheduling your meals. They can eat for 6 to 12 hours, that’s the window to eat or not.

It depends on the individual on how they interpret intermittent fasting. And if they’re influenced by blogs, web pages, and then other doctors or allied healthcare individuals… they use it for their bestselling book reference.

There’s a BBC documentary that shows the high influence in the community about intermittent fasting’s effect on weight change, cardiovascular risk matters, so the community’s thinking is influenced.

There are also alternative intermittent fasting days. Today, I can eat anything and tomorrow, I fast. It depends.

There have been studies done on animals. For humans, only short-term studies. There is no established scientific study for humans on intermittent fasting, weight loss, and the studies are only short-term. There are studies that indicate significant weight change. There are also studies that show advantages for diabetes. But it’s still a short-term study that isn’t applicable for humans, only mice.

Where do I begin if I want to do intermittent fast and is it safe to try?

We encourage people to adapt the normal weight loss program. Even if you talk about the ketogenic diet, I refuse to give a sample diet for the ketogenic diet because it’s a diet specifically indicated for epilepsy – that’s how it’s accepted in science, not for weight loss.

It’s the same for intermittent fasting, we change our body clock. Normally, your intake is 3 meals and snacks. Our body responds with this timing with the healthy individual. [But] if you change your eating pattern, there will still be adjustments. If you change your adjustment tomorrow and you suddenly only eat 500 calories, you will feel dizziness, you’ll get hypoglycemia. Your blood sugar will go down even if you aren’t diabetic. And then if you eat a lot, you will begin producing insulin to compensate for the glucose.

We don’t really encourage intermittent fasting because the it disrupts the functions of carbohydrates, protein, fats. If you’re going to talk about the role of carbohydrates, then it supplies glucose [which] is the main source of energy and it plays a huge role in our brains. If you don’t have glucose because you fasted, you won’t get enough nutrients for your brain and body. Fats and protein then supplies our energy if you’re deficient in carbohydrates.

Intermittent fasting, [the kind where you eat normally for 5 days and restrict for 2 days], it’s fine but you are taking calories beyond your needs. Weight loss will happen but it’s not the correct way of losing weight.

[So it is safe to try intermittent fasting?] no, unless you have excuses that must be accepted [for different reasons] – for instance, Ramadan, religious beliefs, Holy Week, there are many ways of applying fasting. Those are cultural practices.

If anybody insists on intermittent fasting, individuals at-risk should not try this fad diet – pregnant women, children, diabetics, anyone with a disease or a specific condition.

For healthy individuals, be careful but we advice them not to try.

What does intermittent fasting do to your body and will it give short- or long-term effects?

Intermittent fasting is effective for weight loss in a wrong application. Because you lessen your intake for 2 days, so there’s weight loss. But it’s still not applicable because of the health effect.

We don’t encourage people to try intermittent fasting because they will suffer from nausea, lowering of blood sugar. Intermittent fasting is not balanced.

If you fast, even for 2 days, and you only get 25% of your energy needs, then the other macronutrients like protein and fats will assist to produce energy. You change the metabolic pathways of your body. That’s what happens.

How do we produce glucose from protein? Our muscles will the break down to produce glucose, through the help of the liver. Later on, fats will act. Fats will backup as ketones and that’s not a normal process. Only epileptic patients are encouraged to produce ketones because of their brain conditions.

What’s your advice for those who still want to try intermittent fasting?

My advice is not to think of intermittent fasting. [Instead] lead a proper healthy lifestyle. If you are ready to try intermittent fasting, spend your time and effort to know the correct methods of weight loss because you have to consider the long-term effects. If you’re going to consider the intermittent fasting approach, it will only be short-term.

[Instead], have a proper diet and check on the long-term effects, it should have a positive outcome – not just on your health status but also expenses.

Consult with a registered nutritionist, dietician in considering your preferences for weight loss. –