Intermittent fasting - Blog - Persona Nutrition

Intermittent fasting

An alarm clock sits next to a plate with a blue measuring tape piled on top.

Intermittent fasting is a diet that has recently gained just as much popularity as it has skepticism and criticism. Some swear by it claiming that this is not just a fad diet, but a life-altering approach to food. Others are not so quick to jump to the same conclusions. Either way, it’s intriguing for a diet to be so polarizing and it definitely makes me want to know more. So what is intermittent fasting and what does the research really say about it?


What is intermittent fasting?

Intermittent fasting is a type of diet that is characterized by a restriction of caloric intake usually for 12 hours or more. (5) It revolves around the idea that you can alter your metabolism’s normal routine to get the desired results. Sounds crazy, right? To alter one of the most complex functions in your body by simply adjusting your eating times? Although it sounds crazy, there is some truth here! The principal is that by fasting for long periods of time you are forcing your body to make a “metabolic shift” that usually occurs after 12 hours of not eating. (1, 6) This metabolic shift forces your body to stop utilizing glucose as its’ primary energy source and use fatty-acids instead, which is said to reduce muscle loss. (1)

Not only does intermittent fasting focus on the metabolic shift, but its’ other main driving principle is the creation of a caloric deficit. (5) This idea in the nutrition community is much more simple and widely proven that creating a caloric deficit will result in weight loss. So from the metabolism perspective so far we can see how there is evidence that suggests this diet could be beneficial.


What are the potential benefits?

There have been numerous research studies with rats that have shown promising results for the benefits of intermittent fasting. These potential benefits include reduced inflammation, improved glucose metabolism, improved cardiovascular health, increased resistance to disease and stress on cells, and reduced blood pressure. (1) There have also been preclinical studies and clinical trials showing benefits related to diabetes, certain cancers, and neurologic disorders. (2) In a 2018 review of the health benefits associated with fasting, they found that most studies showed a reduction in cardiovascular factors that indicate an increased risk for heart disease. (1) In other animal studies, there has been a link to certain types of fasting and delayed onset of Alzheimer’s and Parkinson’s disease. (2)

All of these benefits sound great! Well, yes, in theory. But a lot of these studies with clearly defined benefits have only been conducted on animals and not humans. Unfortunately, we don’t have enough studies on humans or long-term studies on humans to determine if these benefits are still evident. Yes, some research does suggest that this diet can have many benefits, but on the contrary, there is a ton of research that has not been conducted yet and this diet has just simply not been studied long enough to know the long-term effects on human health.


What are the potential drawbacks?

Despite its benefits, there are multiple potential drawbacks with following this diet such as feeling dizzy, nauseous, light-headed, and fatigued after a fasting period. It also could reduce your exercise performance as you do not have proper nourishment throughout the day to fuel your workout as you normally would. Additionally, you may overindulge on the days that you are not fasting, creating unhealthy eating patterns due to your appetite hormones flaring after a period with very limited to no food intake for long periods of time. (7) There are also possibilities of weight regain, binge-eating disorder, and depression as food is just as much emotional and social as it is for nourishing our bodies. (8)

There is so much information on intermittent fasting that it can be hard to know where to begin and what to believe! However, it’s impossible to determine a diet as solely “good” or “bad” and recommend a diet for everyone or recommend it for no one because the science is so complicated and no one person is the same. There are so many factors that affect everyone’s individual outcomes even with the same approach toward food. Factors like your age, gender, genetics, lifestyle choice, and preexisting conditions can all greatly influence your body’s reaction to different diets. Nutrition is not a one size fits all approach, which is why it can be hard to figure out what is right for you. This also makes the research complex without the possibility of absolute black and white truths.

Despite some promising benefits in research studies, there are still a lot of unknowns about this diet. In general, this diet is not recommended for those who are pregnant, have diabetes, or are on medications. (5) Always contact your RDN and healthcare provider before starting a new diet to see what is best for you and your complex health profile.


  1. Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018;26(2):254‐268. doi:10.1002/oby.22065
  2. Cabo, Rafael De, and Mark P. Mattson. “Effects of Intermittent Fasting on Health, Aging, and Disease.” New England Journal of Medicine, vol. 381, no. 26, 2019, pp. 2541–2551., doi:10.1056/nejmra1905136.
  3. Tello, Monique. “Intermittent Fasting: Surprising Update.” Harvard Health Blog, 10 Feb. 2020,
  4. Gordon, Barbara. “What Is Intermittent Fasting.” EatRight, 7 May 2019,
  5. Orenstein, Beth W. “Intermittent Fasting: The Key to Long-Term Weight Loss?” Today’s Dietitian, Dec. 2014,
  6. Brody, Jane E. “The Benefits of Intermittent Fasting.” The New York Times, The New York Times, 17 Feb. 2020,
  7. Harvard Health Publishing. “Not so Fast: Pros and Cons of the Newest Diet Trend.” Harvard Health, Oct. 2017,
  8. Stockman MC, Thomas D, Burke J, Apovian CM. Intermittent Fasting: Is the Wait Worth the Weight?. Curr Obes Rep. 2018;7(2):172‐185. doi:10.1007/s13679-018-0308-9

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