Time to try intermittent fasting?

Anyone who's tried different weight-loss diets is probably familiar with their pitfalls. Low-calorie diets often leave you tired, hungry, and cranky, often referred to as "hangry." Low-carb or "keto" diets can cause headaches and fatigue, as well as cravings and constipation. Low-fat diets are tough to follow and may not provide much cardiovascular benefit.

Another diet trend, intermittent fasting, takes a different approach. Rather than limiting what you eat, this diet limits when you eat. For some people, this change may be easier to manage.

Short-term studies suggest that people stick to intermittent fasting as well as or better than they do to other dietary habits. Several randomized trials have found that intermittent fasting leads to modest weight loss and may reduce risk factors linked to heart disease, including diabetes, high blood pressure, unhealthy blood lipid levels, and inflammation.

However, experts note that we don't have a lot of evidence about the success of intermittent fasting over the long term; most trials last for 12 months or less. Also, there aren't large populations of people following this eating pattern for years. That's in contrast to two other diets linked to a healthy heart and healthy body size - the Mediterranean diet and a vegetarian diet.

An evolutionary advantage?

Even without the long-term research, people who are overweight or obese could consider giving intermittent fasting a try. In addition to its apparent heart-related benefits, this diet has some unique aspects that might explain its success.

First, the strategy makes sense from an evolutionary standpoint. As early humans evolved, food supplies were alternately abundant and scarce. We also evolved to sync up with the natural day-night cycle, so our metabolism adapted to function best with periods of hunger and eating during the day and fasting and sleeping at night.

Many studies show that nighttime eating is closely linked to weight gain and diabetes. A 2023 study found that women (but not men) who ate their last meal after 9 p.m. were at an increased risk for heart disease and stroke.

Second, intermittent fasting highlights some of the positive aspects of other diet strategies while avoiding their downsides. Focusing on eating only during certain times may naturally reduce calorie intake, and the structure of intermittent fasting may make it easier for people to recognize their eating habits. Finally, because people are not constantly counting calories and feeling deprived every day, the diet is easier to maintain.

Burning stored fat

Periodic fasting triggers the same fat-burning process that occurs during a low-carbohydrate or ketogenic (andamp;ldquo;keto") diet. Ketosis is the metabolic process that kicks in when your body runs out of glucose (its preferred energy source) and starts burning stored fat. Your body may go into ketosis after just 12 hours of not eating, which many people do overnight before they "break fast" with a morning meal. (A midnight snack obviously sabotages this process.)

A keto diet keeps you in ketosis for much longer time periods because you avoid carbohydrates, which supply glucose. Instead, fat becomes the preferred fuel source.

But some nutrition experts worry that keto diets - which can include hefty amounts of saturated fat - may be tough on the heart. Intermittent fasting may be a healthier option, especially if you eat a balanced diet that includes whole grains, nuts, legumes, fruits, and vegetables, which are rich in nutrients known to lower heart disease risk.

However, intermittent fasting diets typically don't specify what foods to eat. Eating mainly fast foods and processed foods wouldn't be healthy, no matter the timing.

As with any diet, it's often a good idea to ease into the changes. Once you have tested out intermittent fasting and start losing weight, you can gradually introduce more healthy foods.

Don't expect fast results, however. With intermittent fasting, people tend to lose weight fairly slowly - about a half-pound to one pound per week. But when it comes to losing weight, slow and steady is more successful and sustainable over the long term.

Before you try intermittent fasting

If you want to give intermittent fasting a try, make sure to discuss it with your primary care provider first. Skipping meals and severely limiting calories can be dangerous for people with certain conditions, such as diabetes. Some people who take medications for blood pressure or heart disease also may be more prone to imbalances of sodium, potassium, and other minerals during longer-than-normal periods without food.

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