If losing weight were simple, there would be one way to do it. But it’s not, which is why there are so many diets that claim they are the best way to shed pounds. Included on that lengthy list are calorie restriction and fasting diets.
They may seem similar, but they have significant differences. The National Institutes of Health describes calorie restriction as reducing average daily caloric intake below what is typical or habitual, without malnutrition or deprivation of essential nutrients. In a fasting diet, a person does not eat at all or severely limits intake during certain times of the day, week or month. One practical effect of a fasting diet may be fewer calories because there is less time for regular eating.
Since most weight loss programs include lowering calorie intake, is either of these better for healthy, long-term weight loss?
Different Forms of Calorie Restriction and Fasting
The NIH says calorie restriction is a consistent pattern of reducing average daily caloric intake, while fasting focuses on the frequency of eating. A fasting diet may include calorie restriction during nonfasting times, but it also may not.
There are several types of fasting diets, also called intermittent fasting:
— Time-restricted feeding. Meals are taken only within a limited number of hours (such as six to eight hours) each day, with nothing consumed during the other hours.
— Alternate-day fasting. No or minimal calories can be consumed one day, and eating is unrestricted the next day.
— 5:2 eating plan. Eating is unrestricted for five straight days, with two days of restricted caloric intake.
— Periodic fasting. Caloric intake is restricted for various times, such as five days in a row once a month, while all other days are unrestricted.
What’s the Evidence?
Some study results suggest that calorie restriction may have health benefits for humans. For example, the National Institute on Aging conducted a clinical trial called Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy. In this study, 218 young and middle-aged, normal-weight or moderately overweight adults were randomly divided into two groups. People in the experimental group were told to eat 25% fewer calories per day than they regularly consumed for two years, while those in the control group followed their usual diet.
The first group failed to meet the target, but managed to reduce daily caloric intake by 12%. Doing that, though, was enough to maintain, on average, a 10% loss in body weight over two years. In addition, those in the calorie-restriction group had reduced risk factors, like lower blood pressure and lower cholesterol, for diseases such as diabetes, stroke and heart disease, and decreases in some inflammatory factors and thyroid hormones.
According to the NIH, only a few studies have examined intermittent fasting. A 2018 review in Current Obesity Report found that, although the data suggest that intermittent fasting “may be a promising weight loss method,” trials have been “of moderate sample size and limited duration.”
Overall, the NIH says that, “Despite a lot of research on calorie restriction and fasting, there are no firm conclusions about the benefits for human health.”
Pros and Cons
There are some factors to consider before jumping into one of these eating plans.”Reducing calories too quickly or too radically can lead to sluggishness, fatigue, irritability, headache, poor sleep and hunger,” says Melissa Majumdar, a registered dietitian in Decatur, Georgia, and bariatric coordinator at Emory University Hospital Midtown. “We often forget that calories are a measurement of energy, and if we reduce calories past the point of the energy our body requires, we will notice a change in energy.”
Majumdar, a spokesperson for the Academy of Nutrition and Dietetics, adds that reducing calories gradually and focusing on choosing nutrient-dense foods (foods that contain vitamins, minerals, fiber and more nutrients) instead of energy-dense foods (which contain a lot of “empty” calories such as added fats and sugars and fewer nutrients), may help you feel more energetic. Or as Abby Greenspun, a registered dietitian in Westport, Connecticut, puts it, “100 calories of Oreos is not equivalent to 100 calories walnuts. You have to look at the quality of the calories.”
As for fasting, when you eat has been linked to health and weight, Majumdar says. Eating is associated with our natural circadian rhythms, and studies have shown that shift workers have higher rates of obesity and health conditions such as diabetes and heart disease, she says.
“There is emerging evidence to support that meal timing may impact metabolic functions like glucose tolerance and insulin sensitivity, and cortisol (stress hormone) levels, which can impact weight regulation. A proposed reason for this is our organs that help manage metabolism, like the liver and pancreas, have light/dark phases linked to our circadian rhythms. If those rhythms are not in line with our eating, weight can be impacted,” Majumdar explains.
Greenspun says that limiting calories at night can make a difference. Reducing late-night snacking is a key weight loss strategy, so she tells her clients to adopt a “close the kitchen time” of 8 p.m. “The body heals and regenerates overnight, so you don’t want to be using that energy to break down food at night,” she says.
[Read: How to Reset Your Healthy Diet.]
Weight Loss the Right Way
As with all diets, these two eating strategies are not the solution for sustained, healthy weight loss. “Everybody wants a magic answer. Today I had a woman ask if had a magic pill, I swear,” Greenspun says. “It’s not magic. You have to put in the work. You have to do things that give lasting change. It’s what you do after the 30 days (of a diet). A lot of people don’t want to do that.”
Majumdar encourages her clients to find an eating plan that has an overall goal of “increasing health, without the only goal being weight loss, that meets their lifestyle. Redistributing food and thinking about the balance of food at meals and snacks can work for many people; it provides nourishment without hunger,” she says.
There is lots of solid scientific evidence that other actions can help you lose weight and stay healthy. The NIH recommends:
— Eat a balanced, nutritious diet in moderate amounts.
— Engage in regular physical activity.
— Drink alcohol moderately or not at all.
— Maintain an active social lifestyle.
— Get a good night’s sleep.
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