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Weighing the Pros and Cons

For thousands of years, fasting has played a major role in religion and medicine. In fact, even ancient Egyptians and Greeks fasted for disease prevention. More recently, however, fasting is being touted as a weight loss technique. Decode the truth behind fasting and find the answer to the ultimate question — is it good for you?

What Is Intermittent Fasting?

Intermittent fasting (IF) is limiting caloric intake to certain time periods. Laura McIntyre, MD, a family medicine physician at Northwestern Medicine, suggests establishing a window of time during which you can eat.

Some types of IF diets include:

  • The 5:2 diet. Five days a week, you eat whatever you’d like. Then, for two days, you eat lightly (around 500 calories or less).
  • The 16:8 diet. For 16 hours each day, you have nothing but water. Then, you eat normally during the remaining 8 hours.

Weighing the Risks and Benefits

Regular fasting has been linked to certain benefits, including:

  • Weight loss. In addition to the reduction in caloric intake, you may lose weight due to lowered insulin levels and increased growth hormones.
  • Improved brain health. IF encourages the release of the brain hormone BDNF and may help protect against neurological diseases like Alzheimer’s disease.
  • Reduced risk for heart disease. Research has shown that individuals who practiced IF experienced lower blood pressure, which lowered their heart disease risk.
  • Decreased risk for chronic disease. IF has been shown to reduce oxidative stress, which causes inflammation. This helps protect against rheumatic disease and chronic pain syndromes.

Potential side effects or risks include:

  • Dizziness or lightheadedness.
  • Headaches.
  • Trouble concentrating.

“These suggest you’re not tolerating fasting,” says Dr. McIntyre. All of these side effects are likely due to dehydration, especially if you’re following a dry fast. “If symptoms occur, you should stop fasting. If you want to try it again, be sure to be well hydrated before and during the fasting.” These side effects can also be a sign of hypoglycemia, or low blood sugar, which can occur when you eat less.

To increase your chances of tolerating a fast, be sure you drink plenty of water and, when you do eat, focus on nutrient-dense foods, because vitamin and mineral deficiencies can occur with a dramatic decrease in food intake. “Focus on getting your calories from healthy sources, like fruits and vegetables,” says Dr. McIntyre.

The Bottom Line

Could something that has been around since ancient times offer promising benefits today? The research is ongoing, though there is evidence to support certain health claims. Research has also shown a surprising link between eating and your body’s circadian rhythm. Eating late at night and poor sleep could increase your insulin levels, leading to weight gain.

If you’re thinking about trying IF, it’s important to know that skipping meals can be dangerous for people with certain conditions, like diabetes. If you have an existing health condition, consult your physician before starting IF.

Laura McIntyre, MD
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