Fasting
When we fast we use up our carbohydrate stores and our liver begins to produce ketone bodies. This is the smell of acetone that we have on our breath after a period of fasting. Two important ketone bodies are called beta-hydroxybutyrate (BOB) and acetoacetate (AA).
When we fast our mitochondria become very slightly stressed. This stress response is a positive effect and prepares the cells for action. This means that when faced with bigger stressors like chemicals and infection, the body is ready to respond.
There are different definitions of fasting. The most general is Calorie Restriction (CR), whereby we cut down the amount of calories we eat by 30-40%. This may help with weight loss in the short term but in the long term can prove difficult because of feeling hungry all the time. CR long term is also associated with osteoporosis, anaemia, heart palpitations and feeling cold.
Other types of fasting that mimic calorie restriction may be just as beneficial but with fewer side effects. Intermittent fasting (IF) is as the name suggests where one fasts for intermittent periods, for example on alternate days. The 5:2 diet is an example of this, where 500-600 calories are consumed on fast days and a more typical diet on non-fast days. Periodic fasting (PF) is where one fasts for a period of time, typically between 1-3 days. It can take 3-6 weeks for the body to get used to fasting, with mood swings being a feature of the habituation period. Older people that fast and lose too much muscle mass are at increased risk of infections.
Time restricted feeding (TRF) is another type of fast where food consumption is restricted to a certain time frame such as a four hour time period during the day. The overnight fast is an especially important fasting period for the mitochondria to recover from their day time work of converting sugar into energy. People vary with how much they need this overnight fast to be. Too short a period and insulin levels will stay high which eventually lead to the development of the metabolic syndrome which features high blood pressure, diabetes and high cholesterol.
Finding the fasting window that suits you is key to understanding your metabolism. I call this the metabolic fasting window (MFW). For some people, this may be as short as seven hours, for others, it may be 12-18 hours. This is especially the case in people that are overweight or have diabetes. A regular fast or fasting period is essential for mitochondria to maintain optimum health.