Intermittent fasting involves cycling between periods of eating and fasting.
Proponents say intermittent fasting is a safe and effective way to lose weight and improve your health. They claim that it’s easier to adhere to than other diets, and offers more flexibility than traditional calorie-restricted diets. “Intermittent fasting is a means of reducing calories by restricting one’s intake for several days each week, and then eating regularly the rest of the days, rather than focusing on permanent caloric restriction,” says Lisa Jones, a registered dietitian based in Philadelphia.
It’s important to keep in mind that intermittent fasting is a concept, not a specific diet.
“Intermittent fasting is an umbrella term for an eating pattern that includes periods of fasting and non-fasting over defined periods of time,” says Anna Kippen, a registered dietitian based in Cleveland. “There are different forms of intermittent fasting.”
One of the more popular approaches is called time-restricted eating. It calls for eating only during an eight-hour window, and fasting the remaining 16 hours of the day. “It can help to decrease our calories but also allows our gut and hormones the ability to rest between meals during our ‘fast,'” Kippen says.
Another popular approach is the 5:2 plan, in which you follow a normal, healthy meal pattern for five days a week. The other two days a week, you consume only one meal of between 500 and 700 calories each day. “This allows our body to rest as well as cut down on calories we consume as a whole throughout the week,” Kippen says.
“Preclinical and clinical trials have shown that intermittent fasting has broad-spectrum benefits for many health conditions, such as obesity, (diabetes), cardiovascular disease cancers and neurologic disorders,” according to a study published in the New England Journal of Medicine in 2019. Clinical research has focused primarily on overweight young and middle-aged adults, the study says.
Whatever method of intermittent fasting you choose, it’s important to apply the same fundamental nutrition principles to intermittent fasting as to other healthy eating plans, says Ryan Maciel, a registered dietitian and head dietitian and performance coach with Catalyst Fitness & Performance in Cambridge, Massachusetts.
“In fact, these (principles) may be even more critical since you are going for more extended periods without food, which can result in overeating for some people,” Maciel says.
Here are principles you should adhere to if you’re on an intermittent fasting regimen:
— Consume minimally processed foods most of the time.
— Create flavorful, delicious meals that you enjoy.
— Eat your meals slowly and mindfully, until you’re satisfied.
Intermittent fasting diets don’t mandate specific menus. However, adhering to good eating principles, there are certain types of foods it’s best to consume and avoid.
Here are three foods to eat on an intermittent fasting diet:
— Lean proteins.
Eating lean protein keeps you feeling full longer than consuming other foods and will help you maintain or build muscle, Maciel says.
Here are five lean, healthy protein sources:
— Chicken breast.
— Plain Greek yogurt.
— Beans, peas and lentils.
— Fish and shellfish.
— Tofu and tempeh.
As with any eating regimen, it’s important to consume highly nutritious foods while intermittent fasting. Fruits and vegetables are typically packed with vitamins, minerals, phytonutrients (plant nutrients) and fiber. These vitamins, minerals and nutrients can help lower cholesterol levels, control blood sugar levels and maintain bowel health. Another plus: fruits and vegetables are low in calories.
The government’s 2020-25 Dietary Guidelines for Americans recommend that for a 2,000-calorie-a-day diet, most people should eat about 2 cups of fruit on a daily basis.
Here are 10 healthy fruits to consume during intermittent fasting:
Vegetables can be an important part of an intermittent fasting regimen. Research shows that a diet rich in leafy greens may reduce your risk of heart disease, Type 2 diabetes, cancer, cognitive decline and more. The government’s 2020-25 Dietary Guidelines for Americans recommend that for a 2,000-calorie-a-day diet, most people should eat 2.5 cups of vegetables on a daily basis.
Here are six vegetables that would be good to consume as part of a healthy intermittent eating regimen:
— Collard greens.
Foods to Avoid
There are certain foods that aren’t good to consume as part of an intermittent fasting regimen. You should stay away from foods that are calorie-dense and contain high amounts of sugar, fat and salt. “They won’t fill you up after a fast, and can even make you hungrier,” Maciel says. “They also provide little to no nutrients.”
To maintain a healthy intermittent eating regimen, avoid these foods:
— Snack chips.
— Microwave popcorn.
You should also avoid foods that are high in added sugar. Sugar that comes in processed foods and drinks is devoid of nutrition and amounts to sweet, empty calories, which is not what you’re seeking if you’re fasting intermittently, Maciel says. “They will make you hungry since the sugar metabolizes super-fast,” he says.
Sugary foods to avoid if you’re engaging in intermittent fasting include:
— Barbecue sauce and ketchup.
— Fruit juice.
— Sugary cereals and granola.
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Update 03/11/21: This article was previously published and has been updated with new information.