Fasting for 24 Hours: What Happens to Your Blood Sugar?

Gone are the days when people used to fast only for religious reasons. In fact, fasting for 24 hours has emerged as a wellness trend. It is believed to have the potential to reset the body, help in weight loss, and improve metabolic health. But as you abstain from food, your body goes through significant internal shifts, especially regarding how it regulates and manages blood sugar. Our medical expert breaks down the biological changes that happen inside a body due to a 24-hour fast, what happens to your blood sugar levels, and how to fast safely.

Let us take a look at what Dr Brunda MS, Senior Consultant, Internal Medicine, Aster CMI Hospital, Bangalore has to say about it.

What Happens to Your Blood Sugar When You Fast For 24 Hours?

Dr Brunda explains the changes that happens inside your body during a 24-hour fast:

• Your body gradually changes the way it gets energy. This is because after the food you have eaten is digested,  blood sugar levels begin to fall slightly.
• Then the body first uses stored glucose called glycogen from the liver to maintain normal blood sugar levels.
• After this, it starts using stored fat for energy, producing substances called ketones, while hormones such as glucagon increase and insulin levels decrease to help release stored energy. 

“In healthy adults, these changes are usually well regulated, but some people may experience hunger, tiredness, headache, dizziness, irritability, difficulty concentrating, or mild weakness, especially if they are not used to fasting,” shares the expert.

Can a 24-hour Fast Harm Your Health?

Dr Brunda says that for most healthy people, a 24-hour fast does not usually cause dangerously low blood sugar because the liver continuously releases glucose into the bloodstream. However, such is not the case with everyone.

The expert shares that fasting can be harmful for certain individuals such as: 

• People with diabetes.
• Those taking insulin or blood sugar-lowering medicines.
• Pregnant or breastfeeding women.
• Children.
• Older adults who are frail.
• Individuals with certain medical conditions should avoid prolonged fasting unless advised and monitored by a healthcare professional, as they may develop hypoglycaemia (low blood sugar), dehydration, or other complications that require prompt medical attention.

Benefits and Risks of Fasting

A 2023 study, titled 'Physiology, Fasting', which was published in National Center for Biotechnology Information (NCBI), shares how fasting triggers significant metabolic adaptations. It shares some of the benefits of fasting:

• One of the primary benefits is improved insulin sensitivity, which helps protect against metabolic syndrome and diabetes.
• Intermittent and prolonged fasting regimens can reduce body fat, lower blood pressure, and decrease atherogenic lipids.
• Animal studies have highlighted that fasting may delay the progression of neurological disorders such as Alzheimer's and Parkinson's disease.
• At the cellular level, fasting inhibits the tyrosine kinase enzyme, a mechanism that holds potential for combined use with cancer treatments. 

The research also highlighted some of the health risk of fasting:

• During the initial fasting period, individuals may experience headaches, which are likely caused by hypoglycemia, dehydration, caffeine withdrawal, or pro-inflammatory pathways.
• Intense or prolonged fasting can lead to excess exposure to glucocorticoids such as cortisol. This may lead to muscle atrophy and paradoxical insulin resistance.
• The study also noted that there is not enough data regarding the safety of fasting in underweight, paediatric, and geriatric populations. 

The study strongly recommended that prolonged fasting should always be performed under the supervision of a health professional. 

Tips To Fast Safely

Dr Brunda shares some tips to fast safely:

• Drink enough water.
• Avoid excessive physical activity if you feel weak.
• Break the fast with a balanced meal containing protein, whole grains, healthy fats, fruits, and vegetables, rather than overeating sugary or highly processed foods. This is because this helps prevent sudden blood sugar spikes and digestive discomfort.
• Some studies suggest that intermittent fasting may improve insulin sensitivity and support weight management in certain individuals.
• It is not suitable for everyone, and long-term health depends more on a balanced diet, regular exercise, adequate sleep, stress management, and following medical advice than on occasional prolonged fasting alone.

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Conclusion

In healthy individuals, a 24-hour fast leads to a natural and well-regulated shift in the body. It burns glucose and stored fat for energy, without causing dangerously low blood sugar. However, prolonged fasting is not recommended, as it can pose serious health risks for those with medical conditions such as diabetes. Therefore, it is advisable to consult a doctor before starting a fasting regimen, and prioritise hydration along with a balanced diet to ensure you are supporting your body's long-term health.