Intermittent fasting seemed to come onto the scene fast and strong in recent years. If I remember correctly, the first time I heard about it was in grad school in 2017. A fellow student in my research class presented on the topic of intermittent fasting (IF) because he had been practicing it and was a firm believer in its benefits. Fasting has been around since the beginning of mankind. People have been practicing fasting on religious holidays or for other spiritual reasons for ages. The IF you have probably heard about, though, is not done for religious reasons, but for health reasons.
I have known quite a few people who have tried out IF. Some only followed this way of eating temporarily and some have been following IF for years. If you do not know what IF is, let me explain. The idea behind IF is that if you restrict the amount of time you dedicate to eating then you will eat less and subsequently lose weight and/or improve health conditions like diabetes. There are different ways to follow IF:
Time-restricted fasting: Eating within a window of time during the day (say 8-10 hours) then avoiding any intake the remaining 14-16 hours of the day and night. Perhaps you would eat only from 10:00 AM to 6:00 PM if following a 16:8 IF ratio (fasting for 16 hours, eating only in an 8 hour window). Other options include 12:12, 14:10, or the more intense 18: 6 (fasting for 18 hours, eating only in a 6 hour window).
Alternate fasting: Alternating eating days with fasting days. The fasting days last a full 24 hours. You could structure this however you wanted. You could eat for a full day (breakfast through dinner) then fast for the entire next day and not eat again until breakfast the following day. Or, you could eat breakfast and lunch on an eating day then fast until lunch on the following day, just as long as you fast for 24 hours.
Modified fasting: Restricting food/fasting for a full 24 hours two days per week and eating normally the other five days of the week. On the two days you fast, you would be allowed to take in 500 total calories for the day, either in one meal or in multiple snacks.
Now that you know the different types of IF, let's delve into the research. As previously mentioned, many people are drawn to IF as a way to reach weight loss goals. However, most research suggests that the real benefits of IF do not have to do with weight loss but with improving health conditions like diabetes, heart disease, cancer and neurological disorders (NOTE: the bulk of the research has been done on animals, not humans - here is a good research article if interested). The reason for the health improvements is due to the metabolic change from using sugar floating around in the bloodstream for energy to using ketones. Ketones are molecules produced by breaking down fatty acids in the body, as well as some amino acids. The process of creating ketones, or ketogenesis, is used in times of fasting and/or starvation. So, to summarize, when you are fasting your body will burn fat cells in order to produce ketones which are then used for energy so you can perform your daily tasks.
One of the good things about IF is that it typically means no nighttime eating or snacking, which gets a lot of people in trouble (myself included). Nighttime eating has been researched and associated with increased rates of obesity and insulin resistance, as well as elevated lipid levels. If a person has trouble consistently resisting sugary snacks late at night or after dinner then perhaps IF would be a good approach to avoiding those extra unneeded calories. That is, if that person knew for sure that the reason for their weight gain or health conditions was solely because of nighttime snacking. Which leads me to a common issue I see with diets: perceived diet benefits can be misunderstood. This is a bit confusing to type out, but I'll do my best. I do not know this as 100% fact, but I feel confident in saying that the main reason people start a diet is to lose weight. Typically, people become overweight or obese due to a long-term pattern of calorie intake that exceeds calorie (or energy) expenditure. People see quick weight loss results from diets like the keto diet, the paleo diet and IF and then glorify those diets as the sole reason for their success. While the diet certainly was at least a catalyst for weight loss, the real reason for the weight loss is a bit deeper than that. If a person goes on the Whole 30 diet after a lifetime of eating mostly fast food, processed foods and sugary drinks then OF COURSE he or she is going to lose weight. Why? Because Whole 30 focuses on eating only whole food sources from the earth and avoiding any processed foods at all. If a person simply decided to stop eating processed foods and only eat whole foods on his or her own (without a structured diet like Whole 30) then I would be willing to bet money that he or she would lose significant weight and feel one million times better at the same time. The same goes for IF and other diets that focus on whole foods. If I lost you, what I am basically trying to say is that going on a diet is not the only way to succeed in losing weight. The harsh reality is that while structured diets offer quick weight loss results, the weight probably will not stay off forever.
Sorry about the soapbox and slight digression. Still with me? Ok, thanks!
The people I have known who have tried IF have done so in an effort to lose weight, and they have been able to do so and keep it off! This is because IF works for their schedules, goals and even personalities. Like any diet or eating pattern, IF will not be for everyone. A person with a history of an eating disorder should steer clear of IF due to its restrictive nature. If a person recovering from anorexia nervosa were to try IF he or she may be reminded of old habits and revert back to a pattern of excessive food restriction. A person with a low body weight may also want to avoid IF due to probable weight loss that will result. Some people may find IF to be too difficult to follow consistently enough to see results. While some enjoy the organization of only eating within a window of time, others may find this window stressful. Intermittent fasting will work for some but not for all.
Once again, my goal as a registered dietitian is to provide you with the nutrition science. After that, it is up to you. You decide what you put into your body, whether or not you exercise, what time you go to bed every night, and how you deal with stress. If you are like me, you want to know all of the facts before making a decision and you do tons of research before making many of your big decisions. I like to do new things on my own and only ask for help if I absolutely have to. I don't necessarily recommend that approach. If you are wanting to lose weight and are unsure what to do or where to begin then working with a registered dietitian would probably be very beneficial for you. An RD can educate you further on nutrition science and various diets, like IF, if you want to try one out. An RD can also educate you on intuitive eating and other non-diet approaches to weight loss.
I want to close with a quote I recently read for the first time:
"Dietitians do not teach people how to diet. Dietitians teach people how to eat".
-Brittany
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