Fasting and Blood Glucose | Jason Fung

Summary

This video delves into the 'dawn phenomenon,' explaining why blood sugar levels may rise during fasting despite the absence of food intake. It highlights the role of hormones like noradrenaline, growth hormone, and cortisol, which counteract insulin and release stored glucose into the bloodstream. The script also addresses concerns about low blood sugar during fasting, emphasizing the body's ability to maintain glucose levels through mechanisms like glycogen conversion and gluconeogenesis. It reassures viewers that fasting-induced blood sugar fluctuations are normal and part of the body's energy management, especially important for those with type 2 diabetes on medication.

Takeaways

• 🌅 The 'dawn phenomenon' refers to the natural rise in blood sugar levels in the early morning due to the body's release of counter-regulatory hormones.
• 🩸 Blood sugar levels may rise during fasting because the body releases stored glucose into the bloodstream for energy, a process counter to insulin's function.
• 🏠 The body stores excess sugar as glycogen in the liver and as body fat, which can be converted back into glucose when needed during fasting.
• 🔄 Counter-regulatory hormones such as noradrenaline, the sympathetic nervous system, growth hormone, and cortisol are responsible for releasing stored glucose into the blood.
• 🚫 Fasting does not typically cause low blood sugar levels as the body can maintain normal glucose levels by converting glycogen and body fat into sugar.
• 💊 For individuals with type 2 diabetes on medication, fasting may require adjustments to medication to prevent excessively low blood sugar levels.
• 🧠 The brain can use ketones as an alternative energy source during fasting, which helps to prevent symptoms even when blood sugar levels are low.
• 🔎 Historical studies have shown that even after prolonged fasting, blood sugar levels can be artificially lowered without causing symptoms due to the body's adaptability.
• ⚖️ If blood sugar levels rise during fasting, it may indicate that the body has excess glucose stores, and fasting is helping to release and utilize this glucose.
• 👨‍⚕️ It's crucial for individuals with diabetes to consult with their healthcare provider when making significant dietary changes, including fasting, to adjust medication as needed.

Q & A

What is the dawn phenomenon and how does it relate to blood sugar levels?

The dawn phenomenon refers to the natural rise in blood sugar levels that occurs in the early morning, around 4 or 5 a.m., due to the body's release of counter-regulatory hormones as part of its circadian rhythm. This prepares the body for the day ahead by releasing stored glucose into the bloodstream.

Why does blood sugar sometimes increase during fasting?

Blood sugar can increase during fasting because the body releases glucose from its storage in the liver and fat cells to maintain energy levels. This is a normal physiological response to ensure the body has energy even when no food is consumed.

What are counter-regulatory hormones, and how do they affect blood sugar?

Counter-regulatory hormones, such as noradrenaline, the sympathetic nervous system, growth hormone, and cortisol, work against insulin. They increase when fasting and signal the body to release stored glucose back into the bloodstream, which can raise blood sugar levels.

How does the body store excess glucose when eating?

The body stores excess glucose as glycogen in the liver and as body fat. This acts as a reservoir of energy that can be converted back into glucose when needed, such as during fasting.

Can fasting cause low blood sugar levels, and why?

Fasting does not typically cause low blood sugar levels because the body can convert stored glycogen and body fat into glucose. In extreme cases, it can also perform gluconeogenesis, converting proteins into glucose. However, people taking diabetes medications need to be cautious as fasting can interact with their medication and potentially cause low blood sugar.

What is the significance of the study where men were fasted for 30 to 60 days and given insulin?

This study demonstrated that even with insulin-induced low blood sugar levels, individuals who had been fasting for an extended period did not experience symptoms or discomfort. This suggests that the body can adapt to using alternative energy sources, like ketones, during fasting.

Why might someone's blood sugar rise very high in the morning despite not eating?

A high blood sugar rise in the morning, especially in people with type 2 diabetes, can be a variation of the dawn phenomenon. It indicates that the body is releasing a lot of stored glucose into the bloodstream, possibly because it had excess glucose stored away.

How should someone with diabetes adjust their medication if they plan to fast?

People with diabetes should consult their doctor before fasting, as adjustments to their medication may be necessary. If blood glucose tends to go too low during fasting, it might indicate that they are over-medicated, and a reduction in medication is needed.

What is the role of ketones in energy metabolism during fasting?

Ketones serve as an alternative source of energy for the brain during fasting. As blood glucose levels decrease, ketones become a primary energy source, allowing the body to function normally even when blood sugar is low.

What does it mean if blood glucose goes up during fasting, and should one be concerned?

An increase in blood glucose during fasting is not abnormal and indicates that the body is releasing stored glucose. It's a sign that fasting is working, allowing the body to use its own stored energy. It's generally not a cause for concern unless the levels are consistently high, in which case one should consult a healthcare provider.