Is Fasting a Safe Way to Lose Weight?

You may be seeing a lot about fasting lately, as this eating practice has become a recent trend for losing weight. But does it work and is it safe? First, let’s talk about what it is.

What is it?

Essentially intermittent fasting (IF) is eating in a specific block of time (4-8 hours) during the day while alternating periods of fasting (16–48 hours) with little to no food. There are many variations of this! Honestly, some of you probably do this on accident at times, such as skipping meals because you are just busy. This eating pattern is not magical, and no one variation is superior. Just like any other “diet”, it is simply another way to decrease calorie intake that may, or may not work for you.

Let’s get to the cons first

  • Lack of evidence. There is not much proof that IF has unique metabolic benefits. Again it is not magic, and fasting in itself, eating windows, or periods of fasting is not what causes fat loss. It is STILL an overall reduction in calories intake at the end of the day.
  • May not be sustainable. If you choose to be on any rigid or restrictive plan, it can interfere with your day to day life. Eating with your family, social occasions, or not being able to enjoy a meal because you “need to fast”. Consistency matters, and yo-yo dieting is not the end goal. Any diet change should be more flexible for a sustainable approach.
  • Potential backfire. Don’t fix what’s not broken. If you enjoy your normal time 3-6 meals a day and it’s what works with your schedule, the traditional portion control/choosing more whole foods will yield the same results. Attempting to ignore your hunger cues may backfire.
  • Risk of binge eating. This approach may CAUSE binge eating or even fat gain. This can happen with dieting because rigid rules or severe restrictions in your intake are highly correlated with binge eating. Just because we are eating in a smaller window or eating less, does not mean our habits—such as the foods we are choosing, sleep, stress or amount of physical activity—are healthier. These are much better predictors of successful weight management.
  • It can be harmful for some. Individuals with certain conditions should not attempt fasting. If you’ve had an eating disorder or signs of disordered eating, which include (but aren’t limited to) binge eating, food obsession, misuse of laxatives and extreme food restriction. But also even if you do not think you have an eating disorder, notice signs of disordered eating, you should contact a professional. If you’re pregnant or breastfeeding, you should not attempt to diet. Anyone being treated for diabetes (with medications) as well as anyone with cancer and those with a compromised immune system should also avoid intermittent fasting. I also would not recommend this style of eating for any athletes or those with heavy training schedules; food is fuel!

Now on to the pros

  • May be more natural for some. People who find eating ‘less often’ easier than ‘eating less’ could especially benefit from trying IF. Some people are just genuinely not hungry in the morning, or are so busy at certain portions of the day that they are skipping meals anyway. I am not promoting meal skipping, but is not harmful for the average healthy person. If it helps one to minimize snacking, or decrease mindless eating, by default they are managing their calorie intake without too much added stress. It is false that eating 6 times a day increases your metabolism! Yes, there is a thermic effect of digesting food, but it is minimal at the end of the day. So if someone can feel good and still be eating enough food on 1-2 meals a day, or in a smaller window, and it helps them be more consistent, then stick to that.
  • Raises awareness of social eating pressures. There does seem to be a societal pressure to eat at certain times of the day instead of listening to our actual hunger cues. This goes both ways of eating when we think we should, or not eating when we think we shouldn’t, despite what our body is telling us.
  • Offers some flexibility. This is not a black and white approach. If you find success with a different eating pattern, it does not mean you have to follow it religiously. If you typically skip breakfast, but have a family brunch you would like to join, going off your normal eating window is not an issue. Staying flexible in your approach (because of our hunger changes, life changes, and schedules change) will be much more sustainable.

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A Better Approach

The key to healthy eating is to listen to your hunger cues and eating healthy, whole foods. On a scale of “thanksgiving full” to “hangry,” you should typically be somewhere in the middle. This can help balance blood sugar and prevent over eating. Maybe keep a food journal to figure out what times of day or situations you are eating just to eat, instead of when you are actually hungry. Mindlessly eating is often the real culprit.

If you aren’t already, cook at home more often. The more whole foods and normal portions, the better. Start with eating more fruits and veggies. “Several fruits and veggies a day keeps the doctor away” is the real saying. 😉

Bottom Line:

NO: Everyone should try it
YES: It can be a useful tool
YES: It can benefit one’s adherence
NO: It is magical


Liz Satterthwaite, RDN, LDN, is a ProMedica dietitian. 

References

Collier, R. (June 2013). Intermittent fasting: The science of going without. Canadian Medical Association: CMAJ, E363-E364.
Patel, K. (2018, April 25). The lowdown on intermittment fasting. Retrieved from Examine.com: https://examine.com/nutrition/the-low-down-on-intermittent-fasting/
Wendy Foulds Mathes, P. K. (March 2009). The Biology of Binge Eating. National Institutes of Health, 545-553.

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