Intermittent Fasting vs. Other Diets: Which Is Best?

Intermittent fasting (IF) is a term used to describe diets that include periods of food restriction. These "fasting" phases are strategically alternated with periods of "feasting" where people who follow the plan consume foods without limitation. Those who practice intermittent fasting restrict or completely eliminate food intake during certain times of the day, week, or month to gain health benefits, boost longevity, or lose weight. Some people also practice intermittent fasting for religious or spiritual reasons.

If you are considering going on an intermittent fasting program, it may be helpful to evaluate how it compares to other similar diets and to nutrition guidelines provided by the USDA.

USDA Recommendations

If you follow an intermittent fasting program, it is unlikely that you will be able to meet nutritional guidelines provided by the USDA on a daily basis. However, it may be possible to reach some guidelines over the course of a week.

Calories

If you follow a time-restricted intermittent fasting plan, you may be able to meet USDA guidelines for recommended caloric intake. Time-restricted IF plans allow you to consume normal meals during certain hours of the day and fast during other hours of the day. These plans generally provide a 6–8-hour window in which to get the caloric energy you need.

However, other types of intermittent fasting will not allow you to meet your caloric needs on certain days of the week. For example, plans such as alternate-day fasting or the 5:2 plan (five days of typical eating and two days of restricted food intake) limit food intake so much on fasting days that you may only get a fraction of your necessary calories for the day.

Other examples of intermittent fasting are the 16/8 method, eat/stop/eat, alternate-day fasting, and Ramadan. The 16/8 method involves fasting for 14-16 hours per day and has an eating window of 8-10 hours. Eat/stop/eat is another method where you have 2 days of the week where you fast for 24 hours. Alternate-day fasting is when you eat normally for one day and then eat little to no calories the next day. Ramadan is a holy month of fasting observed by those who practice the Muslim faith. They fast from sunrise to sunset. This form of fasting is the most studied.

For people who typically consume too many calories, these fasting plans may help them achieve a healthier weekly caloric intake. Caloric intake is very low on fasting days. A 2011 study that compared intermittent fasting with continuous caloric restrictions in obese and menopausal women showed that both are equally effective for weight loss.

USDA guidelines for caloric intake are based on age, gender, height, and activity level. If you are unsure of the number of calories you should consume per day, you can use a calorie calculator.

Food Groups

There are no recommended food groups on an intermittent fasting plan and no food groups are off limits. However, on fasting days, it will be very difficult (if not impossible) to consume the recommended intake of certain food groups (but that's the point).

For example, on the 5:2 plan, a healthy woman is advised to consume 500 calories per day on fasting days. The USDA recommends that a healthy woman consume 130 grams of carbohydrate. Meeting her USDA recommended carb intake alone puts her over 500 calories. Therefore she would have no room to consume protein or healthy fat.

Additionally, some intermittent plans advise a complete fast (virtually no calories) on fasting days. On those plans, someone following the plan would not be able to reach any USDA recommended intake guidelines.

Even over the course of the week, it would be hard for someone to meet the recommended intake of foods like fruits and vegetables. According to data collected by the Centers for Disease Control, only about 12 percent of Americans eat enough vegetables per day and only nine percent eat enough fruit. Only 1 in 10 Americans consumes enough fruits and vegetables per day. On an intermittent fasting program, your intake would have to be substantially higher on feasting days to compensate for days when eating is off-limits.

Variety

Food variety is a great benefit of intermittent fasting. No food or types of food are discouraged so people who follow the eating plan can experiment and enjoy any food that they want.

However, no healthy eating guidelines, cooking methods, or shopping guidelines are provided on most plans. So, if you are a consumer who eats a wide variety of processed foods with added sugars or refined grains, you are likely to continue to eat those types of unhealthy food.

Similar Diets

There are not many commercial diets or eating styles that include periods of complete fasting days. But there are some popular diets that include phases of food restriction.

3-Day Diet

The 3-Day Diet is a collection of diets that require you to severely limit your food intake for three days. For example, people who follow the 3-Day Military Diet consume meals with just a handful of foods that supply limited calories.

Ease and Convenience: Most 3-days diets require you to follow a specific meal plan for the duration of the program. In most cases, this requires you to shop for and measure foods like vanilla ice cream, hot dogs, saltines, or grapefruit. This may not be convenient for some consumers.

Nutrition: As a general rule, many 3-day diets do not provide the calories or nutrition that your body needs. Most limit caloric intake to 1,000 calories or less. Additionally, it would be impossible to stick to these diets and get your recommended intake of fruits, vegetables, and other nutritious foods. When consuming less than 1,200 calories per day, it is very difficult to obtain your vitamins and minerals from foods, alone. Following this diet will require supplementation and assistance from a health professional like a registered dietitian nutritionist.

Health Benefits: Programs lasting just three days are not likely to provide any sustainable health benefits. In fact, going on and off restricted eating programs may even lead to binge eating or other eating disorders. There are no clinical studies to support the effectiveness of this diet.

Weight Loss: While you might notice some weight loss after following a 3-day diet, it is not likely to be sustainable. A diet that is modified for only three days is not likely to result in fat loss. Rather, consumers are likely to lose water weight and protein and may regain the weight in fat after they resume their typical eating patterns.

Body Reset Diet

The Body Reset Diet was developed by celebrity fitness trainer Harley Pasternak. The 15-day diet requires that you go through an introductory phase in which food is restricted. During the first five-day phase you drink only liquid smoothies and forgo solid food. This part of the diet has a fasting feel to it.

Ease and Convenience: Because the program only lasts 15 days, it is important that you follow the protocol very closely to get results. For most of the time, you consume liquid smoothies instead of whole-food meals. During weeks two and three you also incorporate some healthy solid foods.

For some people, it may be a challenge to avoid whole foods at mealtime and just drink smoothies. Also, exercise recommendations are provided. While the recommendations are reasonable, drastically changing your diet and increasing daily activity at the same time might be difficult for some people.

Nutrition: Your caloric intake on the Body Reset Diet will be lower than most recommended guidelines. In fact, during phase one, you are likely to consume less than 1,200 calories per day. However, you will consume a healthy balance of carbs, healthy fats, and protein to help you feel satiated. Recommended foods provide fiber and other healthy nutrients.

Health Benefits: This diet only lasts for 15 days. In that short period of time, you are not likely to gain any sustainable health benefits. However, the program does promote an active lifestyle and provides recommendations for transitioning off the plan. If you follow the recommendations and limit your intake of processed foods, red meat, and other unhealthy items you may improve your health. However, no clinical studies have been conducted.

Weight Loss: It is very possible that you will lose weight on this program—especially if you were sedentary and at a high-calorie diet before starting the diet. Again, however, sticking to the program for only 15 days is not likely to provide results that you can maintain.

Fast Diet

The Fast Diet is a variation of intermittent fasting developed by Michael Mosley, a UK journalist with medical training. The eating program follows a 5:2 eating style where calories are restricted two days each week and you eat a "typical" diet on five days each week.

Ease and Convenience: For some people, this diet may be a challenge to follow because the fasting days are not followed by "feasting" days. In fact, on the days when you are not fasting, you are advised to follow calorie-restriction guidelines and consume only enough calories to meet your energy needs. No foods are off limits and some limited indulgences are allowed, but many consumers who enjoy intermittent fasting do so because they don't have to count calories and because they can indulge without restriction on their non-fasting days.

Nutrition: Healthy foods are recommended on this plan. But fasting days on this diet require that you consume about 25 percent of your recommended daily caloric intake. For women, that is about 500 calories and for men, that is about 600 calories. It would be impossible to get your recommended intake of important nutrients and stay within that range.

Health Benefits: Some studies that have investigated intermittent fasting have suggested that these plans may boost longevity, provide heart health benefits, and help people with diabetes manage blood sugar. But more long-term studies are needed to confirm these benefits.

Weight Loss: Most studies that have investigated intermittent fasting (including plans similar to this 5:2 plan) have shown that weight loss is likely to occur. However, studies have also shown that the results are not necessarily better than traditional daily calorie restriction. Additionally, long-term studies are needed to find out if weight loss is sustainable.

Master Cleanse Lemonade Diet

This restrictive eating plan boasts that you can lose 10 pounds in 20 days.

Ease and Convenience: While the program is simple, it is not easy to follow. Those who follow the plan drink saltwater and a lemonade-like beverage throughout the day for 10 days. In the evening, they drink tea that has laxative effects. Eliminating solid food completely is very difficult for most people.

Nutrition: The extreme calorie restriction on this program make it impossible for you to meet your recommended intake of calories or nutrients. On the Master Cleanse Lemonade Diet, you are likely to consume only 650 calories each day—far less than the recommended intake.

Health Benefits: A short-term, highly restrictive program like this is not likely to yield any health benefits. In fact, you may experience health problems while on the diet. Fatigue, headaches, and dizziness may occur from calorie restriction. In addition, binge eating may happen as a result of extreme hunger.

Weight Loss: Any diet that eliminates solid food and restricts calories to 650/day is likely to cause weight loss. However, weight loss is not likely to be sustainable when you return to your normal eating habits. Such restrictions can also cause electrolyte imbalances, hair loss, and increases the risk for gallstones. In addition, if you overeat after going on the program, you may end up gaining more weight than you lost.

A Word From Verywell

Intermittent fasting diets have shown some promise in the health and nutrition community. However, more research is needed before we know for sure if the eating style is safe for the long-term and if people are likely to maintain the eating style to continue to reap benefits.

Also, keep in mind that simply adding fasting days or fasting hours to your eating regime doesn't necessarily make your diet healthy. If you choose nutritious foods during your feasting days, you are likely to gain health benefits. However, if you overindulge on your feast days or consume less nutritious foods, you are not likely to see the health benefits that you hope for.