What is Intermittent Fasting and Is It Right for Me?
Intermittent fasting is surging in popularity, but do its benefits really hold up to scrutiny? Learn how intermittent fasting works and whether it’s a safe method for losing weight after 50 and your lifestyle.
What Is Intermittent Fasting?
Intermittent fasting recently surged in popularity, becoming the #1 most searched diet in 2019 according to Google. However, fasting is an ancient practice found in cultures around the world. Religious traditions including Christianity, Islam, Buddhism, Hinduism, and Judaism all include intermittent fasting of some sort. Fasting as a weight loss strategy is a newer invention, though there have been reports of fasting therapies for more than 100 years.
At its most basic level, intermittent fasting means alternating between periods of eating and periods of abstaining completely from food. The details and restrictions vary from plan to plan. Proponents of intermittent fasting say that it is one of the most effective weight loss methods available.
There is a large body of science supporting the use of intermittent fasting, though much of it has been done on laboratory animals. To understand why intermittent fasting works, it is helpful to review how our body uses energy. There are three primary sources of energy for humans: carbohydrates, proteins, and fats. Our body breaks down carbohydrates from bread, pasta, or sugar into the building block glucose. Cells then use glucose to power their activities. The hormone insulin helps to move glucose from the bloodstream into cells. Any remaining glucose gets stored as fat.
In most situations, glucose remains our primary energy source. That means our bodies typically run on carbohydrates. If your body is running low on carbs, it will tell your liver to release some more. In some situations, though, it is possible to force your body to burn fat instead of carbohydrates. Fasting causes your body to convert fat into usable energy in the form of ketones. A very low carb diet such as the keto diet is one way to trigger this process, known as ketosis. Intermittent fasting is another.
Different Types of Intermittent Fasting
As the popularity of intermittent fasting increases, there are more types of fasting diets than ever. However, most of them follow three major methods of intermittent fasting:
1. Alternate day fasting
As its name suggests, alternate day fasting switches between feast days (normal eating) and fast days. Typically, a person eats whenever they feel hungry during the 24-hour feast day period. During the following 24-hour fasting period, a person should eat no more than 25% of typical energy needs. For someone following a typical 2,000-calorie diet, that would mean no more than 500 calories in a 24-hour period.
Some people who follow alternate day fasting schedules eat nothing at all on their fast days. This is known as a “complete” fast. Others do a modified fast where they eat a very low calorie diet on the fast days. Alternate day fasting is the strictest type of intermittent fasting, as it results in the most fasting days in a week.
2. Whole-day fasting
A whole-day fasting protocol, sometimes called periodic fasting, involves a period of consecutive fasting lasting at least 24 hours. Again, there are several varieties of the diet that people follow. A method called the 5:2 diet was popularized in the United Kingdom in 2012. On this plan, there are 5 days of eating and 2 days of fasting per week. As with alternate day fasting, some people fast completely, only drinking water or unsweetened tea on their fast days. Others limit their caloric consumption to 500-600 calories.
3. Time-restricted feeding
A time-restricted feeding protocol is the least strict form of intermittent fasting, as it involves shorter periods of fasting broken up by feeding times. With this form of the diet, a person only eats during a certain period of time each day. A popular schedule is a 16:8 diet, meaning there are 16 hours of fasting followed by 8 hours of non-fasting. For example, you might fast from 6 p.m. to 10:00 a.m. the next day but eat between 10:00 a.m. and 4:00 p.m.
What types of foods are allowed during a feeding period is hotly contested within the intermittent fasting community. Some people use an “anything goes” approach, meaning that they eat whatever they want during their prescribed feast times. Others advocate a more moderate approach, focusing on low carb diet plans or whole, minimally processed foods. There is not enough research in humans yet to say which approach is best for nutrition.
Health Benefits of Intermittent Fasting
Most studies of intermittent fasting have been performed in non-human animals such as lab mice and rats. These studies show promising effects of intermittent fasting on a range of health conditions. Following are just a few of the purported health benefits of intermittent fasting:
Weight loss. Weight loss is the reason most people turn to intermittent fasting. Scientific studies have shown that people lose between 2 and 10% of their body weight using this method.
Better glycemic control. Intermittent fasting may help people process blood sugar more effectively. The hormone insulin is responsible for shuttling blood sugar into cells, but people with prediabetes and diabetes may become less sensitive to its effects. In one study of obese men with prediabetes, intermittent fasting lowered insulin levels and improved insulin sensitivity.
Improved cognition. In lab animals, intermittent fasting increases learning and memory performance. There is some evidence that people may benefit from intermittent fasting by feeling more alert and mentally sharp. However, long-term studies are needed to determine whether this diet may reduce risk of cognitive problems like Alzheimer’s disease.
Better physical performance. Aside from weight loss, intermittent fasting may improve overall physical performance. Studies in lab animals show that intermittent fasting have better physical endurance, improved balance, and better coordination than animals on a typical diet. Results in humans are not as clear, with some studies showing better physical performance and others showing no effect of intermittent fasting.
Lower risk of chronic diseases. One of the most promising benefits of intermittent fasting is its ability to lower risk of serious diseases. Unfortunately, there is not yet clear evidence in humans that this is the case. Certainly intermittent fasting may reduce inflammation, which has been associated with healthy aging as well as conditions like diabetes, cardiovascular disease, Alzheimer’s disease, and cancer. Whether this type of diet actually translates to lower disease risk is an active topic of study.
Taken together, it appears that intermittent fasting has clear benefits for metabolic health and weight loss. One of the biggest downsides of intermittent fasting is that it is difficult to maintain. Research studies on intermittent fasting have dropout rates of up to 40%, meaning that many people may not be able to sustain this diet over the long term. That makes it hard to know how this diet affects health over longer periods of time.
Safety and Side Effects of Intermittent Fasting
Intermittent fasting is not for everyone. While occasional fasting is generally fine for your body, there is very little research about the long-term effects of intermittent fasting on health. Consider the following side effects and concerns about intermittent fasting to make an informed choice.
Side Effects of Intermittent Fasting
Some of the side effects of intermittent fasting develop within a few days of starting the diet plan. On your fast days, you may develop headaches or other pain. You may also feel tired, lethargic, and mentally dull. Intermittent fasting also causes irritability -- after all, it can be uncomfortable not to eat all day! In a clinical research study, adults following an alternate day fasting routine experienced a spike in hunger that lasted for the entire 21 days of the diet. This raises serious concerns about the sustainability of this diet approach.
One way to avoid these side effects of intermittent fasting is to switch to a less rigorous fasting schedule. For example, time-restricted feeding is generally less strict than alternate day or whole day fasting. If these symptoms become distracting or interfere with your daily life, it could be a sign that intermittent fasting is not right for you.
Overeating on “Feast” Days
Another concern about intermittent fasting is that it could cause people to overeat on days or time periods when they do not need to restrict calories. In studies of rodents, this appears to be the case. Rodents on an intermittent fasting regimen actually end up eating as many calories as those allowed to eat whenever they want. The same may be true in people -- if you’ve restricted your caloric intake for 16 hours or a full day, you’re likely to overeat when you are finally allowed to eat again. This may hamper your ability to lose weight while following an intermittent fasting meal plan.
Effect on Chronic Health Problems and Medication Absorption
One of the attractive benefits of intermittent fasting is that it claims to reduce insulin sensitivity. This can be helpful for overall blood sugar regulation and reduction in your risk of diabetes. However, intermittent fasting may not be the best approach for people who already have diabetes, heart disease, or other chronic health conditions. Skipping meals can cause fluctuations in blood sugar that may be dangerous for diabetics. Fasting may also make people more prone to electrolyte imbalances. This is particularly dangerous for people with heart problems, as they need to maintain healthy levels of sodium, potassium, and other minerals.
Finally, intermittent fasting can be problematic for people who take certain medications. Some medications are meant to be taken on a full stomach to avoid stomach irritation, nausea, and too-rapid absorption. Fasting makes it challenging to take these medications as prescribed. That is why experts recommend that people always talk to their medical providers before beginning a strict diet like intermittent fasting.
Fasting and Health for Older Adults
Older people may be particularly vulnerable to negative effects of intermittent fasting. Most studies in humans have focused on younger or middle-aged adults. Older adults have different metabolism rates and unique metabolic needs. For an older adult of average body weight, intermittent fasting could easily cause too much weight loss. This could affect bone health, increasing risk of fractures. It could also impact the immune system.
Take Home Message
Despite its fad status, intermittent fasting may be here to stay as a popular weight loss tool. However, it is extremely important to understand the risks associated with this diet. Failure to follow a healthy eating plan could lead to nutrient deficiencies or ill health. This is particularly true for people trying to lose weight over 50, as older adults have unique diet needs.
The best diet plan is one that you can stick with over the long term. Developing lifelong healthy eating habits is the best way to lose weight, feel better, and improve your quality of life. Mighty Health is here to help you in your journey to better health. As an individualized health coach for 50+, Mighty Health gives you the information you need to make healthier changes. That includes things like eating natural foods, avoiding added sugars, and boosting your healthy fat intake. While this can fit into an intermittent fasting framework, there are often easier and more sustainable diet choices.
If you’re ready to take the next step toward a healthier life, take advantage of the Mighty Health online health coach to get started. We’re here to help you understand facts vs myths when it comes to intermittent fasting and healthy aging.