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What You Need to Know About Intermittent Fasting

Written by: Julie Tang, MS, RDN, CNSC




From Atkins to Paleo, to Whole 30, to several more diets, it’s undeniable that there are many popular diet trends these days. As different as they all are, one thing many of them do have in common is the claim of helping people lose weight and improve their health. One of the today’s most popular diets is intermittent fasting. It’s unlikely that you haven’t already heard someone talk about it.


Intermittent fasting is a diet that involves cycling between eating and fasting. Fasting is known as the intention of not eating or limiting the amount of food eaten for a period of time. This diet has invoked much attention and leaves many people curious of what it is, its benefits and risks and whether it is the right diet for them.


History of intermittent fasting


Intermittent fasting has been around for centuries, but it recently gained popularity over the last decade. Dating back to the hunters and gatherers’ days, there is a belief that fasting may have been unintentionally practiced due to periods of famine when there was no or limited harvest. They would go through periods of time without food. As a result, humans have evolved to be able to adapt to natural cycles of fasting, including when we sleep.


Fasting has also been a regular practice for certain religions as a way for men and women to express their devotion and discipline to their religious practice. Additionally, fasting has been historically seen as a way to reinforce a person’s social and political views through practices such as hunger strikes.


Today, intermittent fasting has made a comeback and people are primarily choosing to practice this approach for health benefits and possibly weight benefits.


What is intermittent fasting?


There are many different methods of intermittent fasting, but all are based around cycling between eating and fasting. Unlike other popular diets that often restrict foods or food groups, intermittent fasting is best described as an eating pattern or schedule that guides when you eat rather than what you eat.


The common methods are:

  • The 16:8 method: This involves restricting food intake for 8 hours a day and fasting for 16 hours, in which no food is eaten. Certain calorie-free liquids such as water, unsweetened tea, and coffee are allowed during the fasting timeframe.

  • The 5:2 method: This involves eating normally for 5 days a week and then limiting consumption to about 400-600 calories a day or about 25% of normal caloric needs for 2 days of the week.

  • Alternative date fasting method: This involves eat normally one day and then limiting consumption to about 400-600 calories or about 25% of normal caloric needs on the following day. The pattern alternates each day.

  • Nonspecific or random fasting: This is when a person does not choose to follow a specific method, but will decide to randomly skip meals, restrict caloric intake or fast for a 24-hour period, once or twice a week. On other days, they would eat as normal.

The most popular form of intermittent fasting is the 16:8 fasting method.

People find it the simplest and most sustainable to do. Another version to this time-restricted method is 14:10, when a person eats within a 10-hour window and fasts the remaining 14 hours.


Some say the time-restricted 16:8 or 14:10 method may help reset our circadian rhythm, also known as our body’s internal clock. Early humans did not always have access to food as most of us do now. There is the argument that today’s convenient access to food around the clock can potentially lead to disruption of the circadian rhythm, possibly contributing to obesity and metabolic diseases such as diabetes and heart disease. By intermittent fasting, it may help “reset” our circadian rhythm and we eat in sync with it.


Is intermittent fasting effective for weight management?


One of the biggest draws to trying intermittent fasting is weight loss. In a few research studies including one conducted by Krista Varady, PhD, an associate professor of kinesiology and nutrition at the University of Illinois at Chicago, researchers found that due to the changes in hormones from short term fasting, there was an increase in metabolic rate. Compared to the effects of long term starvation or other diets that restrict intake, in which metabolic rate is often decreased. This finding could be one of the main proponents of why intermittent fasting may be an effective weight management tool.


Despite recent developments, many health experts argue that there is a need to further understand if intermittent fasting causes our body to be more efficient in using and burning fat cells which can contribute to weight loss. Or is weight loss simply the result of calorie restriction from fasting?


Naturally, when a person fasts by reducing the amount of calories they eat either through skipping meals or eating smaller portions, their overall caloric intake for the week will be lower compared to the caloric intake if they did not fast. As a result, weight loss is the expected outcome as long as calories are not overeaten on days they eat normally.


Effects on our body


Beyond its potential effect on weight, intermittent fasting may provide a few health benefits including lowered insulin resistance, reduced inflammation, improvement in lipid panel and promoting cognitive health.


A study by Rothchild et al (2014) indicated that the findings of animal studies and time-restricted intermittent fasting demonstrated decreased body weight (though not consistently), lower concentrations of triglycerides, glucose, and low-density lipoprotein cholesterol, and increased concentrations of high-density lipoprotein cholesterol.


Another study by Adlouni et al (1997) conducted with healthy males practicing fasting for Ramadan showed a significant decrease in LDL-cholesterol (“bad” cholesterol) and an increase in HDL-cholesterol (“good” cholesterol) after one month of fasting when compared with levels before their fasting.


Studies suggest that fasting may also play a role in improving insulin sensitivity. Insulin is a hormone produced by the pancreas. Its main role is to help cells absorb glucose for energy and this results in lowered glucose in the blood. Having low insulin sensitivity indicates that the cells do not absorb the glucose as well and blood glucose becomes elevated. Long term low insulin sensitivity can increase the risk of type 2 diabetes. Conversely, if a person has high insulin sensitivity, they reduce their risk of type 2 diabetes. Fasting would essentially give the cells a chance to rest from taking in glucose and this can help to improve their sensitivity to sugars over time.


Limitations on research


Despite some promising findings on intermittent fasting and its effects so far, many experts argue that there is still limited research to show the long term effects of intermittent fasting. In addition, many research studies involved animals such as rats and mice, and its outcomes do not necessarily translate to human efficacy.


Intermittent fasting is not for everyone


Is intermittent fasting right for everyone? The answer is no. Determining who should safely try intermittent fasting depends on a person’s health goals, current health status, dietary habits, medical history, mental health and preference of lifestyle. Intermittent fasting can put certain individuals with a medical history at an increased health risk.


This population includes those with diabetes or at risk of high or low blood sugar, women who are pregnant or nursing, people who are underweight and struggling with weight gain, those with a history of disordered eating and those who take medications for blood pressure or heart disease may also be more prone to electrolyte abnormalities from fasting. It is important to stay educated on the risks involved and to consult a provider before trying this diet.


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