Although fasting is medically defined as going without food and drink, you can do a "smoothie fast" by only drinking smoothies for intermittent days to lose weight. To shed pounds, you need to consume fewer calories than you burn off. As long as the strawberry banana smoothies you make result in a calorie deficit by the end of the day, you'll be able to lose weight. If you drink them excessively or use a large amount of high-calorie ingredients, you may take in more calories than you burn off and actually gain weight.
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One cup of whole strawberries is 46 calories, and each medium-sized banana is 105 calories. If you make a smoothie using 2 cups of strawberries and 2 bananas with just water, you have a 300-calorie smoothie. If you wanted to use milk, each cup of nonfat or skim milk is an additional 91 calories. Adding one plain, unsweetened nonfat Greek yogurt container to the mix gives you 100 more calories.
How Much to Drink
Once you've chosen the ingredients in your strawberry banana smoothie and added up the calories, find out how many calories you burn on an average day to make sure you're creating a calorie deficit. The number of calories you expend depends on your weight, height, age and activity level. An average middle-aged man burns anywhere from 2,400 to 3,000 calories a day depending on his activity level, and an average woman burns 2,000 to 2,400. Once you have an estimated number, you can determine how many smoothies you want to drink in a day to maintain a calorie deficit.
There are different ways to fast for weight loss using smoothies. Intermittent fasting is a safe, effective method of fasting for weight loss, done by alternating days of regular eating and days of calorie restriction. For successful weight loss, however, be careful not to overeat on nonfasting days. According to an NPR article published in 2013, one intermittent fasting program consists of eating normally for five days of the week and restricting your caloric intake for two days of the week down to 500 to 1,000 calories. Eating only strawberry banana smoothies would count as the two calorie-restricted days of the week in this program.
Benefits of Liquid Meals
In a study published in "Nutrition Journal" in 2012, obese women who ate a calorie-restricted diet with intermittent fasting not only lost weight, but they also lost fat mass and had reduced cholesterol levels. Women who had calorie-restricted liquid meal replacements, in which liquid meals replaced one or two meals a day, lost more weight than women who had calorie-restricted diets without liquid meals. The benefits of "smoothie fasting" are not limited to weight loss. Drinking liquid meals allows your digestive organs to rest. When your system is not as bogged down breaking down heavy meals, the enzyme activity is redirected to detoxifying the body.
It's important not to fast for too long to make sure you're getting enough nutrition, including micronutrients from a wide variety of foods. Intermittent fasting is better than long-term fasting because you can balance out your diet over a week with the nutrients you need from various foods. You can get your vitamin and mineral levels tested at a clinic to check for deficiencies. It also helps to consult with a certified nutritionist before embarking on a fasting program or any new diet. See your health care provider before doing a "smoothie fast" if you have a medical condition or are taking any medications.