- A 24-hour fast raises LDL and HDL cholesterol temporarily in healthy adults
- Blood glucose drops about 8 mg/dL during a 24-hour fast, improving glycemic control
- Metabolism shifts to fat oxidation and ketone use while lowering energy expenditure
Fasting diets have become extremely popular which involves cycling between eating and fasting. Some of the most popular ones are 16:8 intermittent fasting (fast for 16hrs and eat in 8hr window), 14:10 intermittent fasting, 5:2 diet (eat normally 5 days and very low calories for 2 days), and 24-hour fast (once or twice weekly), among others. These diets are known to have several health benefits, which includes reduced calorie intake, improved blood sugar levels, lower body weight, better cellular repair, and others. However, it is important that you follow these diets under medical supervision.
When you follow a 24-hour fast, once or twice a week, it triggers significant metabolic shifts in the body. Your body adapts to no calorie intake, primarily using stored energy sources. This affects cholesterol, blood sugar, metabolism, and more. Here, take a look at how 24-hour fast affects your cholesterol, blood sugar and metabolism.
Impact Of 24-Hour Fast On Cholesterol, Blood Sugar And Metabolism
Cholesterol
During a 24-hour water-only fast, the total cholesterol rises. This happens due to an increase in both LDL and HDL cholesterol. In one study of 30 healthy adults, LDL climbed 23.1 mg/dL while HDL increased 3.7 mg/dL. Triglycerides drop sharply and this reflects the reduced availability of carb and higher fat mobilisation.
This rise happens due to hormonal changes. The human growth hormone increases which promotes fat breakdown and releases cholesterol from adipocytes. Short-term fasting thus elevates circulating lipids temporarily, but repeated or prolonged fasting (beyond 24 hours) can improve lipid profiles long-term by improving lipoprotein quality and reducing atherogenic risk. This effect reverses quickly upon refeeding in healthy individuals, with cholesterol falling after meals.
Blood Sugar
Blood glucose usually falls during a 24-hour fast, dropping around 8 mg/dL from baseline, along with normalised insulin levels even in untreated type 2 diabetes patients. Glycogenolysis supplies about 167g of glucose, maintaining levels without food. On the other hand, insulin decreases significantly by the end of the fast due to no carb intake.
Pre-fast meal composition also matters. Consuming a high-carb shake spikes glucose and insulin initially, delaying metabolic benefits. However, low-carb/high-fat delays glucose rise and speeds ketosis entry. In older overweight adults, glucose stabilises after 2-3 hours regardless, with continuous monitoring showing minimal fluctuations. Hormones like GLP-1 rise post-fast, which boosts insulin sensitivity 24 hours later. Overall, 24-hour fasting improves glycemic control in the short-term, which is beneficial for prediabetes. However, proper hydration can reduce the risks of hypoglycemia.
Metabolism
A 24-hour fast lowers 24-hour energy expenditure, while preserving the circadian rhythms in expenditure. Fat oxidation increases rapidly, while carb oxidation drops, favouring ketosis.
The body switches fuels. Liver glycogen depletes in 10-14 hours, which prompts lipolysis and ketone production for brain/muscle energy. Weight loss of approximately 1.5 kg occurs mostly from water/glycogen, and not fat. In lean males, prolonged fasting leads to high fat burn without crashing expenditure rhythms. Growth hormone helps to preserve muscle, reducing loss of lean mass. Repeated 24-hour fasts may impact metabolism for better efficiency, improving fat utilisation over time.
Is The 24-Hour Fast Safe For Everyone?
Fasting can be beneficial for weight management, and other chronic conditions. However, it is important to understand that it is not for everyone. Johns Hopkins Medicine says that the following people should steer clear of trying intermittent fasting:
- Children and teens under age 18.
- Women who are pregnant or breastfeeding.
- People with type 1 diabetes who take insulin. While an increasing number of clinical trials have shown that fasting is safe in people with type 2 diabetes, there have been no studies in people with type I diabetes.
- Those with a history of eating disorders.
Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.
