Nutrition / Food

When You Should Avoid Intermittent Fasting

Intermittent fasting is great for some people, but for others it could be dangerous.

For some people, intermittent fasting (IF) is a complete game-changer. It’s the key to everything from sustainable weight loss to increased mental clarity to a serious boost in energy.

But, just because intermittent fasting is the go-to lifestyle for some people doesn’t mean that it’s for everyone. While intermittent fasting is a healthy choice for some, for others, it can actually be dangerous.

But, who exactly should avoid intermittent fasting? What are some of the dangers? And what are some alternatives for people who aren’t the right fit for intermittent fasting—but still want to reap similar benefits?

Insulin-Dependent Diabetics

One population that could put themselves at serious risk by following an intermittent fasting schedule? People who struggle with Type 1 or insulin-dependent diabetes.

“Intermittent fasting cycles between periods of fasting and unrestricted eating. In people living with diabetes and who take anti diabetic medications, especially insulin, this could be very dangerous,” says Dr. Rocio Salas-Whalen, endocrinologist and founder of New York Endocrinology.

“Anti-diabetic medications, specifically insulin, will continue to have an effect on blood sugar on the fasting days. This could drop sugar levels to a dangerous point,” she adds.

Diabetics need to maintain stable blood sugar levels to stay healthy (through both diet and exercise). This can be nearly impossible with intermittent fasting.

Endurance Athletes

Training for a marathon or an upcoming Ironman? If so, intermittent fasting probably isn’t for you.

“Nutrient timing is extremely important for sports performance and would be a challenge while following an intermittent fasting diet,” says Allison Knott, MS, RDN, CSSD, a New York City-based registered dietitian.

“Endurance sports require increased calorie needs because of the excess calories burned. And, the impact [that] endurance exercise has on nutrient needs before, during, and after an event or long training session requires consistent calorie intake and adequate macronutrient intake to repair muscle, replenish glycogen stores, and maintain electrolyte balance.”

Intermittent fasting doesn’t give you the steady dose of calories and nutrients you need to train, perform, and recover. So, if you’ve got an endurance event coming up, you should plan to avoid intermittent fasting. (Follow a more endurance-friendly eating plan, instead).

People With a History of Disordered Eating

If you’re recovering from disordered eating behaviors, intermittent fasting is a no-go. “Some people who will want to avoid intermittent fasting include those with a tendency to disordered eating or a history of an eating disorder,” says Knott.

Intermittent fasting requires periods of restriction followed by periods of eating larger meals. This can be extremely triggering for people who struggle with restricting, binging, or other disordered eating patterns. In such cases, it’s better to avoid intermittent fasting altogether and stick to a more consistent nutrition plan.

Pregnant Women

When you’re carrying a child, you need to follow a pregnancy diet that is filled with nutrients (and calories!) to keep you and your baby healthy. Unfortunately, you won’t get that with intermittent fasting.

“People with chronic conditions, such as diabetes or cancer, would not want to practice intermittent fasting because of the potential for low blood sugar, inadequate calorie intake, and the possibility of not meeting adequate nutrient needs. The same is true for women who are pregnant and breastfeeding because of increased calorie and nutrient needs,” says Knott.

If you’re pregnant, you need to eat often and enough to support you and your baby’s health. The structure of intermittent fasting just doesn’t allow for that.

Are there alternatives to intermittent fasting?

Clearly, intermittent fasting isn’t for everyone. But, if the IF lifestyle isn’t for you, is there a way to reap all the benefits of intermittent fasting (like weight loss, increased energy, optimal fat burning, and better concentration) without putting yourself at risk?

The answer is yes—with a commitment to a healthy, well-balanced lifestyle. And, while that solution might not be as buzz-worthy as the intermittent fasting craze, it can certainly be just as effective.

“Much of what we know about nutrition doesn’t have headline-making appeal because it’s boring. Eat more plants, choose heart healthy fats, eat lean animal proteins (if you want)—but also include plant proteins—focus on variety, drink water, avoid added sugars, limit ultra-processed foods. We all know these things,” says Knott. “The key is to make that way of eating one that makes up the majority of your diet, the majority of the time, and for the majority of your life.”

If you have a condition that prevents you from hopping on board the intermittent fasting train, you can still enjoy all the health-boosting benefits. Make positive changes to your diet that you can commit to sustaining in the long-term.

“As with any diet, the one you can stick to is the one that will have the most impact. Changing your thinking to frame a health behavior as one you’ll have for life will have a positive impact on how you approach any change,” says Knott.

Food Nutrition


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