Intermittent Fasting 101: The Science is Unclear

Intermittent fasting was first discovered in 1945 when scientists realized intermittent fasting extended the lives of mice. However, due to celebrity success stories in the last few years the trend has risen in popularity.  Intermittent fasting is a way of eating where a person rotates periods of eating with periods of not eating, or fasting.  If you type “intermittent fasting” into a search engine, millions of results will come up. Varying web sites will proclaim the value of intermittent fasting for  managing weight loss, heart disease, type 2 diabetes, aging, and sleep problems, however, the science in this area is still lacking, unfortunately. Most of the studies are short term and are limited to obese rats or small groups of people, therefore the findings cannot be applied to the general population at this time. Also, the long term effects and side effects of intermittent fasting are still unknown.

If you think about it, we all fast while we sleep – intermittent fasting just encourages prolonging that fast. A main reason this approach can help with weight loss is that you end up taking in fewer calories than you typically would during the day. This method can also be an effective way to practice listening to your body and better recognize different physical hunger cues.

One moderate approach to intermittent fasting is the 12-hour version, where you limit yourself to eating 3 meals between 7 a.m. and 7 p.m. The main fasting window is during our sleep and not eating after dinner.

Another common but somewhat more restrictive version people are using would be the “16:8,” where you have an 8-hour window for eating and 16 hours of fasting. For example, you might eat between 10 a.m. and 6 p.m or between 11 a.m. and 7 p.m.  People who do not like to eat breakfast tend to follow this method. However, there is not enough research to know if this dietary pattern is a safe and effective way to keep off those extra pounds.

Other popular versions include eating only one meal a day and the “5:2,” where you eat normally 5 days a week and severely restrict your calories on the other 2 days. I would not recommend these approaches, since they are not likely to be sustainable for the long term or safe for some individuals.

No matter the type of intermittent fasting, more research needs to be done in the area. We still do not know all of the negative side effects of intermittent fasting such as the possibility of nutrient deficiencies, dehydration, light-headedness, dizziness, or hypoglycemic episodes. Intermittent fasting may also cause health risks for certain individuals.  It is not recommended for people with diabetes, pregnant women, or women who are breastfeeding. It is also not recommended for people who have a history of disordered eating or eating disorders. It’s a good idea for anyone considering intermittent fasting to consult with their primary care physician, especially if the person is taking any prescription medications.

Some useful takeaways from the intermittent fasting trend are the following:

  • Listen to your own physical hunger/fullness cues.  Eat when physically hungry (stomach growling), and not for emotional reasons (stress, boredom, sadness, anger, etc). Do not eat if not physically hungry.

  • Avoid unnecessary snacking or eating late at night.

  • Intermittent fasting does not address the quality of the diet. The majority of one’s food choices should be packed with vitamins, minerals, fiber, and other nutrients. Making smart food choices can help you stay healthy, manage your weight, and be physically active.


Katie Abbott, MS, RDN, INHC

Author Katie Abbott, MS, RDN, INHC

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