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Are Fasting Weight Loss Plans Safe & Effective?

by | May 8, 2019 | Last updated Feb 15, 2022

Author: Amanda Cofer, MPH

You may have overheard a co-worker in the breakroom or your sister-in-law at a family gathering throw the words “fasting” and “weight loss” into the same sentence. They saw that some celebrity slimmed down for a role this way and they want to shed some pounds too. They’re “feeling great” have “more energy” and have already dropped a handful of pounds! Now you’re thinking, “is this something I should try too?” Before you hop on the fasting for weight loss bandwagon let’s breakdown the safety of these plans and their effectiveness. Are fasting weight loss plans safe and effective? The short answer is, it depends, but here are the deets.

What is fasting for weight loss?

Before we dive any deeper, let’s talk about what kind of intermittent fasting plans might be out there. It’s important to note that not every fasting plan is created equal and that some may be more doable than others.

  1. Alternate Day Fasting: fasting that includes alternating between days with no calorie restriction and days where only one meal is eaten that contains roughly 25% of someone’s daily caloric intake.
  2. Whole Day Fasting: 1-2 days per week of complete fasting or only consuming 25% of daily calories with no food restriction on other days of the week. For example,  the 5:2 plan where 2 days are fasting while the other 5 days are not.
  3. Time restricted feeding: following a plan each day that uses a designated time frame for fasting and eating. For example, 16:8 where all of the daily calories are consumed in an 8 hour time from and fasting is done for 16 hours.

If you take a close look at these plans you can clearly see the differences. Some have you skip meals entirely while others cram calories into a few hours in your day. When eating patterns like this are used it’s easy to see a drastic drop in calories which can come with some not so super consequences.  

Fasting for weight loss safety

Right now in the world of research, little is known about intermittent fasting but what is known needs to be considered before using this method for weight loss. Remember to always talk with your healthcare provider before trying anything new. First, our bodies need calories to survive. The word “calorie” may have gotten a bad rap over the years but the truth is that we need them. Think of them as the gas you’d put in your car. Calories fuel our metabolisms, food provides nutrients, so what happens if you choose a fasting plan that seems to cut this out?

Those who fast for weight loss for long periods of time can experience some pretty severe symptoms. Dehydration is a danger while fasting as well as electrolyte imbalances that can lead to other serious conditions. Since much of the food we eat contains vitamins and minerals it’s also likely that those fasting in these situations can experience deficiencies (scurvy is not pretty…). Even on short weight loss fasting periods you may encounter dizziness, fatigue, constipation, and bouts of low blood sugar levels. For those with conditions such as diabetes and high blood pressure, these side effects may be even more dangerous than they are for the average Jane (or Joe). Along with this to consider, fasting for weight loss could actually setback your efforts.

Fasting for weight loss effectiveness

While the effectiveness of fasting for weight loss is still under investigation, there are some findings that you may want to consider before writing out your meal plan. First, remember that sustainability is key for long term weight control and the present studies suggest that fasting probably isn’t a good idea for the long term. Studies that compare fasting to other types of weight control methods seem to experience high drop rates (as high as 65%..yikes) in the fasting groups that may also give insight into how difficult fasting for weight loss actually is.

A randomized control trial (the king of research studies) divided up 100 participants to examine whether or not fasting was more effective for weight loss that traditional routes. With this paper, researchers found absolutely no significant difference between the fasting group and traditional route of calorie management. They also found that those in the fasting group ate less than allotted on their fasting days and more than allotted on their non-fasting days. This gives and insight into one of the pitfalls of weight loss fasting and how fasting can actually shoot your weight loss efforts in the foot, sort of speak. When we cut our fuel source, our bodies respond by conserving energy and our metabolisms all but come to a screeching halt. In the midst of a fast our bodies will dampen appetite to compensate for this but once you lift restrictions, all bets are off. Your appetite is likely to come back with a vengeance due to the biological urge to eat more. Weight loss may happen in the beginning but continuing this type of pattern will have you spinning your wheels in the long run.

Fasting for weight loss: The Bottom Line

In the end, fasting may be give you short term weight loss success but in the long term can be hard on your body, metabolism, and mindset. It’s important to note that the weight loss you do experience while fasting may not last once you go back to your regular eating schedule. If you’re goal is to detox, know that you’re body has some pretty spectacular ways of doing this on it’s own (let your liver and kidneys do their job). Those who fast for weight control also don’t appear to fair any better than those who simply watch what they eat.

When losing weight the main objective should always be to create sustainable lifestyle changes rather than a temporary diet. The Noom app is working to break the cycle of restriction by helping app users do just that! Break free of the diet mindset and start changing your life and your health for good.