What is intermittent fasting
Fasting is an ancient practice that involves avoiding calories for a period of time. It is a simple way to control your weight that doesn’t require you to follow a specific diet, count calories or measure food.
Intermittent fasting schedules
There are many ways to practice intermittent fasting for weight loss. The following are some of the most popular schedules:
This involves consuming all of your meals within a period of 4-12 hours in a day. For example, you could choose to have your meals and calories between 8 am and 6 pm. Limiting your calorie intake to daylight hours is called “eating with the sun”. Time-restricted eating is particularly beneficial if you eat your meals before sunset. Not only does this help you eliminate bad habits like late-night snacking, but it improves your sleep and blood sugar control. Over time, time-restricted eating can lower your blood sugar levels, make you more sensitive to insulin, and reduce your blood pressure.
This involves packing all of your day’s calories in a single meal that you consume within 1-2 hours. A small study showed that fasting for 24 hours 3 times a week and eating only dinner on fasting days, eliminated the need for insulin in type-2 diabetic patients. This fasting approach also resulted in improved HbA1C, lower body mass index, and reduced waist circumference.
This involves alternating between days in which you consume no calories and days in which you eat normally. Another way of looking at ADF is as three 36-hour fasts per week. For example, eat normally on Monday until 6pm. Don’t eat until breakfast on Wednesday morning. Finish dinner by around 6pm Wednesday night. Now don’t eat again until breakfast on Friday. Eat normally the rest of the day and finish dinner by 6pm or so Friday night. Now don’t eat again until breakfast on Sunday. This way of fasting increases life span in rodents by 80%, possibly by decreasing glucose levels and regulating insulin. It also reduces the incidence of cancer in lab animals genetically predisposed to it. Alternate-day fasting is the most studied method of intermittent fasting in humans, and it’s been shown to lead to weight loss and to improve heart health, as it reduces circulating levels of LDL or ‘bad’ cholesterol.
The 5:2 “diet”
The 5:2 plan involves eating normally for five days each week and then fasting for the last two. For example, you might decide to fast Monday and Tuesday and then eat normally the rest of the week. You can also look at it as one 60-hour fast per week. Finish dinner at 6pm on Sunday night and don’t eat again until breakfast on Wednesday morning, for example.
How to do intermittent fasting
If you are just getting started with intermittent fasting, we recommend slowly working up to your target fasting schedule over the course of several weeks or months. Start by reflecting on your eating habits. Do you snack in between meals or after dinner? If so, try a 12-hour fast overnight. This means you finish dinner by 7 pm, for example, and don’t eat anything else until 7 am the next day. If you usually don’t feel the need to eat after dinner or between meals, try a 14-16 hour fast (For example, finish dinner by 6 pm and don’t eat again until 10 am the next day). If you’d like to fast longer, add 1-hour increments every 5 days or so. Drink water to keep you both hydrated and distracted from hunger. If you need caffeine, drink unsweetened black coffee and tea.
What happens to your body during intermittent fasting?
There are many things that happen during intermittent fasting that either don’t happen or that happen very slowly when we are always eating.
When you eat, your cells enter growth mode
In a well-fed state, the individual cell in your body is in “growth” mode. Its insulin signaling and mTOR pathways that tell the cell to grow, divide and synthesize proteins are active. By the way, these pathways, when overactive, have implications in cancer growth.
The “mammalian target of rapamycin” or mTOR loves having plentiful nutrients around, especially carbohydrates and proteins. When active, mTOR tells the cell not to bother with autophagy (literally cellular “self-eating”), a recycling and cleanup process that rids your body of damaged and misfolded proteins, for example. The well-fed cell isn’t worried about being efficient and recycling its components – it’s too busy growing and dividing.
In a well-fed state, your cells and their components are also highly acetylated. This means that various molecules in your cells, including the “packaging” proteins called histones that wrap your DNA up nicely within the core of your cells, are “decorated” with acetyl groups on their lysine (amino acid) residues. Don’t worry if you don’t understand the jargon in that last sentence. What you really need to know is that the well-fed cell has many genes, including those associated with cellular survival and proliferation, turned on. This is because acetylation tends to loosen the packaging proteins that normally keep your DNA wrapped up, and lets your DNA be read for protein production.
While your cells turn on cellular growth and proliferation genes when you aren’t fasting, they also turn other genes off. These include genes related to fat metabolism, stress resistance and damage repair. Actually, with intermittent fasting some of your fat gets turned into ketone bodies that appear to reactivate these genes, leading to lowered inflammation and stress resistance in the brain, for example.
But during starvation, things are very different
When you practice intermittent fasting, your body reacts to what it sees as an environmental stress (low food availability) by changing the expression of genes that are important in protecting you from, well, stress.
We have a well-preserved starvation “program” that kicks our cell into a completely different state when food, particularly glucose or sugar, isn’t around. With intermittent fasting and exercise, you activate the AMPK signaling pathway. AMPK or 5′ AMP-activated protein kinase is the brake to mTOR’s gas pedal. AMPK signals the cell to go into self-protective mode, activating autophagy and fat breakdown. It inhibits mTOR. At the same time, while you are fasting the levels of a molecule called NAD+ begin to rise because you don’t have the dietary proteins and sugars around that normally convert NAD+ to NADH through the Krebs cycle. NAD+, a molecule whose precursor is Vitamin B3, activates the sirtuins, SIRT1 and SIRT3. (Have you heard of the “longevity” molecule in wine called resveratrol? Yep, it became famous as being a potential activator of the sirtuins). These sirtuins are proteins that remove the acetyl groups we talked about above from histones and other proteins. In this process, the sirtuins silence genes related to cell proliferation and activate proteins involved in creating new mitochondria (the power-generating factories of your cells) and cleaning up reactive oxygen species.
Ketones, also produced during fasting, work as deacetylase inhibitors (in other words, keeping acetyl groups in place). This turns on genes related to antioxidant processes and damage repair.
Whew, that’s a lot happening while your body isn’t taking in any calories. But when exactly do these things happen? We’ve helped you visualize the timeline below and in the LIFE Fasting Tracker app, with a series of icons on the LIFE Fasting arc that represent the five stages of intermittent fasting!