You may already know that the dietitians at the Brittany Jones Nutrition Group take an all foods fit approach, but now we are adding all times fit as well!
As dietitians, it is very common to be asked about the newest diet trend (it makes for 50% of our cocktail party conversations). Over the past year, intermittent fasting has been increasing in popularity and interest largely due to social media influencers, celebrities, and TV shows promoting the new trend. When a new diet trend comes out, we are easily distracted by the flashy titles and promised results rather than to refer to the research. Today we are going to discuss evidence and research behind the newest diet trend, explain why we consider it to be a fad diet, and share some of our concerns. Ready? Here we go!
What is IF?
Intermittent fasting (IF) is unique from the other fad diets because it tells you when you can’t eat, but not what you can’t eat like more traditional fad diets. Intermittent fasting is defined as periods of voluntary abstinence from food and drink and is an umbrella term for several different forms of fasting. First, let’s break down the different types of intermittent fasting:
- Complete alternate day fasting involves alternating days of fasting (no consumption of energy-containing foods or beverages, i.e. only water) with eating days (foods and beverages consumed as desired without restriction).
- Modified fasting regimens allow for consumption of 20% to 25% of energy needs on scheduled fasting days and standard eating the other days. The modified fasting regimen is the basis for the more popular 5:2 diet, which involves severe calorie restriction for 2 nonconsecutive days a week and no restricted eating the other 5 days.
- Time-restricted eating allows individuals to consume food within specific windows, which leads to fasting periods on a regular basis. The most popular time-restricted eating is 16:8, in which there are 16 hours of fasting and 8 hours of eating. For example, eating from 8 AM to 4 PM and fasting for the rest of them.
While many of the points discussed in this article can be applied to all forms of fasting, we will be focusing on time-restricted eating as the most common type we are seeing. With all the hype around IF, it is important to remember everyone does some type of fast while they sleep, hence our break-the-fast (breakfast!) in the morning. This is totally normal. However, the time of this fasting can change daily based on your schedule and hunger cues, as opposed to a scheduled intermittent fasting which follows a set schedule and is typically for a longer than normal fasting period.
5 Reasons Intermittent Fasting is a Fad Diet and not a Lifestyle Change:
1. Intermittent fasting is not a magic pill.
Research indicates that weight loss seen from IF is no different than the short-term weight loss achieved by other fad diets. 
“But I have read that intermittent fasting improves blood glucose, lipid levels, and insulin sensitivity too?” Most of the studies done on IF have been performed on animals (not humans) over a short period of time, measuring glucose numbers, rather than long term results. It has long been known that a reduction of weight among overweight individuals decreases blood glucose levels, triglycerides, and blood pressure.  The “mechanism” for the improved lab values seen with IF is driven from the weight loss produced by a caloric deficit, not by the time window an individual consumes or does not consume calories. More research is needed on IF to make this statement true. Keep in mind that for long term improvements in lab values, the lifestyle MUST be sustainable. If you’re only able to follow it for 3 months, your lab values are likely to return to where they were prior to the diet. Keep in mind this research also does not take into account mental health (more to come on this later).
2. It is not a sustainable lifestyle change, and can lead to the diet cycle.
When clients and friends ask us about the newest fad diet, we typically respond with, “Is that something you would like to do for the rest of your life?” Even the research acknowledges the difficulty of IF due to “periods of elevated hunger on fast days, societies with constant, convenient access to nutrients, and eating patterns strongly intertwined with social structures.”  In other words, it is difficult for individuals in the studies to stick to intermittent fasting, even for a brief period of time. Intermittent fasting does not allow flexibility for special events like weddings, vacations, and brunch with friends – let alone for the flexibility needed in everyday life!
Intermittent fasting and all fad diets end up leading to what we call the diet cycle. The inevitable “slip-up” will happen where you eat during your “fasting window,” end up feeling guilty for breaking the food rule, then leading to overeating because of the guilt, and eventually give up all together. Then comes the next fad diet to take its place and start the cycle all over. So many clients we have seen have been caught in this cycle – which is why we promote sustainable lifestyle change for our clients and do not recommend fad diets! Weight cycling or yo-yo dieting also increases inflammation in the body, and increases overall risk for chronic diseases like heart disease, diabetes, and eating disorders.
3. It does not teach you anything about the composition and nutrients in food.
Because IF only focuses on the timing of eating, it ignores the most important aspect of nutrition: the composition of the food you are eating! Fans of IF say one of the biggest pros is that it is easy and you do not have to dive into the details of nutrition. However, weight management (if that’s your goal) and creating a healthy lifestyle takes TIME. Time is needed to learn about why you need to eat a variety of nutrients – rather than following diet rules that can result in malnutrition, decreased energy levels, and more. Intermittent fasting, like many fad diets, skips all the learning that is needed to create a sustainable healthy lifestyle. The more you know how food fuels your body, and how to listen to your body, the healthier you will become – and the longer the results will last.
4. It causes you to ignore your body’s natural hunger cues.
Everyone can probably think of a time they have fasted, either intentionally or not, and the subsequent hunger pains/mood changes that came along with it. Forcing hunger over and over again is neither sustainable nor healthy. Research shows that food restriction decreases baseline dopamine levels, and enhances a higher dopamine release in the brain when you do eat which can lead to overeating.  This means that you are less happy while fasting, and then become overly happy when you eat (leading to a potential binge). An important part of creating a sustainable healthy lifestyle involves being in tune with your body, and IF teaches you to ignore those hunger cues, and then to ignore fullness cues. Other side effects of intermittent fasting include feeling cold, irritable (anyone else get “hangry” over here?!), low energy, feeling distracted, and having reduced work performance – yikes!  Many IF’ers skip breakfast, and according to the Academy of Nutrition and Dietetics, skipping breakfast is associated with higher BMI and increased obesity risk. A balanced breakfast consisting of a carbohydrate paired with a protein/fat starts our metabolism for the day, and also balances our dopamine levels!
5. It can lead to an unhealthy relationship with food, and put you at risk for an eating disorder.
One of the biggest concerns that we have as Registered Dietitians with intermittent fasting is its potential to lead to an eating disorder, or disordered eating. Many people may begin IF with healthy intentions, but their behavior can become an eating disorder due to the restrictive nature of the diet trend. If someone that is driven by the number on the scale or the a desire to look thin starts to restrict eating, say, 16 hours a day, and sees “positive results” it can psychologically lead to fasting even longer, and a worst case scenario that behavior can lead to an eating disorder. Individuals can easily hide an eating disorder behind intermittent fasting as a social excuse to not eat (a warning for health providers and parents!) In a large study of 14-15 year olds, dieting was the most important predictor of a developing eating disorder. Those who dieted moderately were 5x more likely to develop an eating disorder, and those who practiced extreme restriction were 18x more likely to develop an eating disorder than those who did not diet. 
People with anorexia nervosa generally restrict the number of calories and the types of food they eat, and they ignore their bodies natural hunger cues. They tend to be obsessed with weight, calories, food, and dieting and often avoid social situations that involve food.
Our concern is that many of the features seen in anorexia nervosa fall in line with that seen in intermittent fasting.
Binge eating, characterized by eating a larger amount of food in a certain time frame than most people would eat in that same window, can look a lot like IF too because of increased hunger. It’s important to note that not everyone with an eating disorder is classified as “underweight,” and are are still at risk for medical complications and disruptions in mental and social health from disordered eating. Disordered eating is especially of concern for women of child bearing age, as preconception is an important time for women to maximize their nutrient intake and going without eating means going without important energy, protein, vitamins, and minerals. To understand the risk factors and warning signs for the development of an eating disorder, read the Common Signs of an Eating Disorder on the National Eating Disorder Association website: https://www.nationaleatingdisorders.org/warning-signs-and-symptoms
Across the board, the research agrees that there is not enough evidence to recommend intermittent fasting and more research is needed due to the lack of long-term interventions and follow-up periods.
Furthermore, the research has not investigated the dietary quality among fasting individuals and the social, mental, and emotional consequences of fasting. The Instagram influencer with abs may be convincing, but we encourage you to remember the research, and to think about how it would fit into your lifestyle. The Registered Dietitians at the Brittany Jones Nutrition Group are all about focusing on your overall health, including physical, mental, emotional, spiritual, and social. Would intermittent fasting be infringing on one of those aspects of health in your life? We are not promoting snacking through the night, but rather a lifestyle in which you eat enough throughout the day to enable adequate sleep at night, allowing you to wake up rested in the morning and to ‘break-the-fast’ with a nutritious breakfast and set your day up for success.
We are all about making sustainable lifestyle changes that allows for flexibility, focus on friends and family, and enjoying the fun in food and eating!
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- Roseberry, A. G. (2015). Acute fasting increases somatodendritic dopamine release in the ventral tegmental area. Journal of Neurophysiology, 114(2), 1072–1082. doi: 10.1152/jn.01008.2014
- Wolfram, T. (2018, October 4). Investigating Intermittent Fasting: Food & Nutrition: From the Magazine. Retrieved from https://foodandnutrition.org/from-the-magazine/investigating-intermittent-fasting/.
- Golden, N. H., Schneider, M., & Wood, C. (2016). Preventing Obesity and Eating Disorders in Adolescents. Pediatrics, 138(3). doi:10.1542/peds.2016-1649
-Written by Brittany L. Jones, MS, RD, LD and Anna Whitlow, Dietetic Intern