What you need to know before starting intermittent fasting: 5 scientific considerations

Intermittent fasting, or IF, has gained a lot of attention for its potential health benefits as an eating pattern. Some IFers report more energy, weight loss, and improvements in metabolic health. (1) But intermittent fasting isn’t for everyone. There are a few health reasons you might want to think about before you get started.

Some research suggests that people with specific medical conditions, such as those affecting digestion or blood sugar, or those at certain stages of life, should exercise caution before starting intermittent fasting. (4) Let’s break down the research-based considerations to help you decide if intermittent fasting is right for you and your lifestyle.

Medical Conditions and Medications: Who Should Avoid Intermittent Fasting?

Before jumping into intermittent fasting, you should consider your personal medical history and current medications, and as always, talk to your doctor. People with diabetes, kidney stones or gastroesophageal reflux disease should approach fasting with caution and receive personalized advice before starting the fast. (4)(5)

Additionally, if you are taking medications for heart disease, blood sugar, high blood pressure, or medications that require food for proper absorption, intermittent fasting may affect their function or have negative side effects. (6) And anyone with an eating disorder should avoid intermittent fasting, as any type of eating plan can trigger unhealthy patterns of food restriction and overeating. (7)

Health conditions that might make intermittent fasting a bad idea

If you are taking medication for any medical condition, including heart disease, diabetes, high blood pressure, or medications such as insulin and blood thinners that may require regular food intake for proper absorption, intermittent fasting may not be right for you. (6)

Here are other health conditions that could make intermittent fasting the wrong approach for you:

• Diabetes: Fasting affects blood sugar levels, leading to dangerous dips or unpredictable spikes. (4)
• Kidney stone: Fasting may increase the risk of stone formation by affecting hydration status and dietary intake.5)
• Underweight Individuals: Fasting can lead to further weight loss, so it should be done under medical supervision and with regular health checks. (8)
• History of eating disorders: Fasting can lead to unhealthy eating patterns, making it unsafe for those with past or current eating disorders. (7)

Effect of intermittent fasting on metabolism

One of the most discussed benefits of intermittent fasting is its effect on metabolism. Research suggests that fasting triggers fat burning through a process called ketosis. Then the body burns fat for energy in the absence of carbohydrates. (1)

In addition, intermittent fasting can improve insulin sensitivity, potentially reducing the risk of developing type 2 diabetes by lowering blood sugar levels and promoting better glucose control. (9)

However, some significant research points out that when compared to other types of calorie-controlled diets, fasting was not associated with more significant weight loss than other types of calorie-restricted diets. (10)

This means that if you’re not a good candidate for fasting, any type of diet that works for you can still help you reach your weight loss goals.

Another metabolic benefit is autophagy, a cellular repair and regeneration process that occurs with any type of calorie restriction. (11) This process is linked to longevity and may protect against age-related diseases by removing damaged cells. (11)

Hormonal effects: Why fasting may be different for women

Women’s bodies are very sensitive to changes in calorie intake, which is why intermittent fasting can affect female hormones such as estrogen and progesterone. (12)

Research shows that prolonged fasting can disrupt the balance of female reproductive hormones, potentially leading to irregular menstrual cycles and uncomfortable symptoms. (12) Importantly, women trying to conceive may want to avoid long periods of fasting, as calorie restriction can negatively affect fertility. (12)

For women who are pregnant or breastfeeding, fasting can lead to nutrient deficiencies and insufficient calorie intake, which can affect the health of the mother and baby. (13) If you are a woman at this stage of life, consult with your health care team before attempting intermittent fasting.

Even outside of pregnancy, women with hormonal imbalances such as polycystic ovary syndrome (PCOS) should be careful with fasting. It can make symptoms worse. (13)

Finally, some research suggests that women may benefit from shorter fasting periods, such as 12 to 2 p.m. instead of the more restrictive 4 p.m. schedule. (14)

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About experts:

Caroline Thomason is a dietitian and diabetes educator who combines her love of nutrition with the power to make better health easier to understand. With 12 years in the industry, she has published in more than 40 publications, is a CPG consultant and advisor, speaker, broadcast spokesperson and recipe developer.

Joanna Gregg, RD is the food data curator at MyFitnessPal. She received her bachelor’s degree in nutrition from Georgia State University and her master’s degree from the University of Nebraska.

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Cortisol and Stress: The Science of Fasting and the Stress Response

Intermittent fasting can also affect the level of cortisol, a hormone responsible for managing the body’s stress response. (15)

Long periods of fasting can increase cortisol production, especially if you are already stressed or sleep-deprived. (15) Elevated cortisol levels appear to be associated with weight gain, particularly in the abdominal region, which may counteract the weight loss benefits associated with fasting. (16)

Moreover, high cortisol levels can cause stress eating when the fasting period ends, creating a cycle of overeating followed by restrictive fasting. (17) This is one form of disordered eating, and if you fall into this pattern, fasting may not be good for you. (17)

Overall, if you are prone to stress or have difficulty managing stress-related cravings, intermittent fasting may not be the best approach.

Blood sugar sensitivity: who should be careful?

If you have blood sugar problems, such as diabetes or hypoglycemia, you need to be extra careful with intermittent fasting. (4) Although fasting can improve your insulin sensitivity, it can be risky for those with diabetes, as prolonged fasting can lead to dangerously low blood sugar. (9)

Especially if you take insulin or other medications that affect blood glucose, fasting can increase your risk of hypoglycemia, which can cause serious symptoms such as dizziness, brain fog, confusion, or fainting. (18)

Even for those without diabetes, long periods of fasting can cause blood sugar to drop, leading to irritability or a general feeling of fatigue. (19) If you have a blood sugar-related condition, consider a shorter fast or talk to a health care professional to find the safest approach for you.

Bottom Line: Is Intermittent Fasting Right for You?

Although intermittent fasting has gained popularity for its potential benefits for metabolic health, it is not right for everyone. Before you jump in, consider how fasting can affect your hormones, metabolism, stress levels, and blood sugar regulation.

With any new diet, consult a health professional such as a dietitian or your doctor. If fasting isn’t for you, there are endless options for your meal plan to help you reach your goals.

And if you decide to try it, definitely take a look Intermittent Fasting Tractor within the MyFitnessPal app.

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