There’s a lot of hype at the moment about intermittent fasting and time- restricted eating. There’s also a lot of conflicting information out there. In this post I have explored whether this way of eating offers a safe, effective and long term way to gain health and lose weight.
Note, I am not a nutritional expert, or dietician, but there’s a lot of crossover in the work I do. Also, diet is, of course, such an important factor in wellbeing and fitness. Plus weight loss is a hot topic at the moment with the government’s push to tackle the obesity crisis. I therefore want to try to understand the topic from an evidence based perspective.
What’s the difference between intermittent fasting and time-restricted eating?
Intermittent fasting means not consuming food or drink, other than water, for longer than a normal overnight period of 8-12 hours. This could be fasting for entire days, which some programmes advocate, or extending the food-free window to 16 hours for example. Time-restricted eating is the term given to restricting food intake to certain times or hours during the day.
I personally do not like the idea of whole days without food intake (although the body can survive for days without food and we are evolutionarily programmed to go without food for a certain amount of time). I know some weight loss programmes advocate 1 day on and 1 day off food entirely. I’m more of a supporter of intermittent fasting during the night whereby we give the body a nice long rest from food intake for at least 12 hours. I think this is sensible, good for us and most importantly completely achievable and sustainable for most people.
It’s worth noting that if you have a history with an eating disorder then intermittent fasting for long periods of time may not be advisable. It’s always worth seeking medical advice if you are unsure.
Physiologically what happens when we give our bodies a break from food intake?
Giving your body a break from food or drink (other than water) will do amazing things and will provide a whole host of health benefits. After 6 or 8 hours the body’s natural glycogen stores will have been used up and the body will start to utilise fat sources. Your body will then start to burn fat which has previously been inaccessible. Over twelve hours a process called autophagy kicks in.
I read about this in Dr Rangan Chatterjee’s book The 4 Pillar Plan. Dr Chatterjee refers to the work of biologist Yoshinori Ohsumi who focuses his research on autophagy or “oxidative damage”. It is basically the body’s internal way of sorting out and clearing up internal mess and clutter. The body starts to repair cell damage, the immune system and many other essential functions. As Dr Chatterjee says:
“Eating all your food in a restricted time window – for example, within twelve hours – allows your body to enhance it’s own natural house-cleaning…during the fasting period, the liver is helping to repair our bodies and burn off fat!”.
Dr Rangan Chatterjee The 4 Pillar Plan
Snacking, insulin levels and weight loss
Dr Fung talks about the science of time restricted eating in his book The Obesity Code. Dr Fung attributes genetics, insulin and hormone imbalances to be the predominant causes of obesity.
In the simplest terms:
- Insulin’s role in the body is to transport sugar, obtained from food, from the blood stream to the body’s cells
- In a fasting state, when insulin levels are low, the body burns stored glycogen and then moves on to burning fat
- When you eat too many sugar or carbohydrate rich foods too often, the body receives a signal to stop any fat burning and burn glucose received from your last meal instead. This keeps insulin levels high
- This means the cells in the body do not respond to insulin receptors and can cease working properly
- The cells become reliant on glucose and over time this can result in insulin resistance, weight gain and obesity
Dr Fung’s research has found that snacking in between meals is a high predictor of insulin resistance. The body ideally needs 4-5 hours rest between meals in order to have regular low levels of insulin. Snacking between meals interrupts this and keeps levels of insulin higher than they need to be.
The hormone leptin serves to make us feel full and the hormone ghrelin makes us feel hungry. Too much insulin also disrupts and confuses the body’s natural hormones so these messages become unclear. This can lead to overeating, weight gain, obesity and other diseases. I.e. the brain fails to recognise when the body is full and the hungry signal may continue when the body is not actually hungry because of the hormonal imbalance. How many times have you heard people who struggle with their weight say they don’t feel full? A hormone imbalance could be the cause.
What is circadian rhythm?
Professor Satchin Panda is an expert in circadian rhythm. His book The Circadian Code, explores how the daily cycles and rhythms we experience impact a huge number of areas in our lives from obesity, weight gain, inflammation, depression, anxiety and even some forms of cancer.
He discusses how there is a circadian clock present in every part of our bodies. Studies have shown that even if a human being is locked away without access to natural light the body will still wake and sleep at similar times. This is because every cell and hormone in the body is programmed with daily cycles of waking up, sleeping and eating. The different areas of the body are primed for these functions at appropriate times of the day. For example, in the middle of the day the digestive system is optimised and during the evening the body is set to become tired and fall asleep.
How does circadian rhythm affect weight loss and diet?
Time-restricted eating and intermittent fasting may encourage eating less food and therefore a reduction in calories consumed. Studies have shown this is the case simply because people are naturally eating for fewer hours in the day.
In a recent Feel Better Live Move podcast with Professor Panda, he talks about experiments with mice which have shown promising results for health and weight control.
In one experiment mice were given a high fat and fructose diet. The mice became obese and suffered cardiovascular disease within 9-10 weeks. They also began to eat when they were not hungry particularly in the middle of the night when the gut and liver are not primed for digestion.
The mice were then divided into two groups. Both were given the same diet and all other conditions were the same. The only difference was that one group were allowed to eat whenever they wanted and the second group were restricted to eating within an 8 hours window. At the end of the experiment the mice eating within the restricted window were protected against diseases such as obesity and cardiovascular disease and mental health conditions.
Professor Panda also discusses a second set of experiments whereby already obese and diabetic mice were placed on a 10 hour restricted eating window. These mice lost 40% of their body weight within a few weeks. They could also outrun mice who were eating a healthy diet on a treadmill.
These findings have been replicated time and time again and clearly show that aligning eating time with circadian rhythm can have huge health benefits. Whilst it’s not completely clear how these experiments would translate into humans, this offers promising research in support of time-restricted eating. Human trials are underway and it’s very exciting to hear what the results may be!
Professor Satchin is conducting a huge worldwide study to examine the role of circadian rhythm in health. To sign up and download the App visit his website here.
Is breakfast really the most important meal of the day?
This is a controversial area as most of us have all grown up believing that we need a hearty breakfast. This is not actually the case, according to experts, and the body can go for hours without needing sustenance in the morning. Indeed, having a later breakfast may be a really good and easy way to extend the fasting period and encourage fat burning. Some experts are even advocating skipping breakfast all together.
However, if you exercise in the morning I’d always make sure you are eating within an hour of finishing. As your body needs nutrients and fuel to repair muscles and recover from your workout.
Top tips for embracing your body’s natural rhythms for optimal weight and health:
- Don’t eat at night – try to eat before 9pm and definitely avoid any late night munchies.
- Try to eat within an 8-12 hour window pushing back breakfast if possible
- Stop snacking between meals to allow insulin levels to drop
- Avoid processed white carbs such as white bread, rice and pasta and swap for wholegrains – brown rice, wholegrain rice.
- Eat a largely plant based diet full of fresh vegetables and fruit
- Exercise for at least 30 mins a day. Exercise can help to deplete glycogen stores even more so combined with time-restricted eating can be a great way to shed the pounds and get into shape.
