Dr Rangan Chatterjee: Change when (not what) you eat to lose weight
In part three of our serialisation of his new book, Dr Rangan Chatterjee explains how a 12-hour eating window can help you shed pounds
One of the most astonishing discoveries weight-loss researchers have made in recent years is that when we eat might be just as important as what we eat. Over the past few years, numerous studies have suggested that if you eat the majority of your calories earlier in the day, you can end up losing more weight than if you eat those same calories later on and into the evening.
Scientists now know that the times of the day we choose to eat, and how often, can have a significant effect on how much weight we put on. This is because the timing and frequency of our food affects the working of our signals.
How snacking disrupts the body’s signals
One reason obesity has been soaring over the last few decades is that we’ve dramatically increased how frequently we’re putting fuel into our systems. Back in the 1970s, most of us ate just three meals per day. But things are very different now.
Our store-fat signals are influenced by the hormone insulin. Whenever we eat, insulin is released, which informs our body that fuel has become available. It instructs the body not to break down the fat it already has on board. So if you’re eating small meals and snacks multiple times a day (especially if they are highly processed), your body is being flooded with regular releases of insulin, which means it is never being allowed to break its own energy stores down and is constantly stuck in the store-fat mode. Essentially, you are never giving your body enough of a break from food to allow it to start burning off your existing fat stores.
Time-restricted eating
We’re not designed to be digesting food all day long. This is why reducing the hours in which we eat to a limited window can be a great idea. In 2018, one set of scientists compared a group of people who ate their meals over an entire day with those who ate all their meals within just eight hours. Remarkably, at the end of eight weeks, the second group, who did all their eating inside a compressed time window, showed a marked reduction in fat, even though the amount of calories eaten was the same between each group.
Rather than changing what they ate, they changed when they ate. Time-restricted eating has proved to be an effective strategy with plenty of my patients, readers and podcast listeners. Many prefer to start off with a 12-hour window (for example, eating between 8am and 8pm), which should be manageable for most, and then move it down to 10 or eight hours. My clinical experience has shown that, in isolation, it may not work for everyone when it comes to losing weight, but I would strongly encourage you to at least go for the 12-hour window. Let’s not forget, this was probably the norm for everyone on Earth as recently as 50 years ago. It’s only because our eating habits have changed so much that we’ve had to give a special name to what’s been a normal part of the human routine forever.
How to do it
- Document when you eat your first bite of food and when you eat your last bite over the course of a week.
- Pick a 12-hour window that fits your lifestyle – for example, have breakfast at 7am and finish dinner by 7pm. Don’t feel disheartened if the first week is tough. Give your body time to adjust. Don’t be afraid to try different eating windows to see if they work better.
- Encourage any other adults in your household to participate. Behaviour change is always easier when other people are involved.
- Pay attention to how you feel when you are eating this way. Does your hunger change? Do you sleep better? Do your symptoms of poor digestion improve? Write down any benefits daily.
- When a 12-hour eating window becomes a doddle, experiment with 11, and then 10. But don’t push it too far beyond your comfort zone because it needs to be sustainable.
- You can drink water, herbal teas and non-sugared black tea or coffee outside your eating window
If you have type 2 diabetes or are on any blood sugar lowering medications, talk to your doctor before you go for prolonged periods without eating.
In addition to fat loss, restricting your eating window may also help you reduce hunger and snacking, improve sleep, improve digestive symptoms like heartburn, stabilise blood sugar, support your immune system, increase energy, reduce inflammation, improve IBS symptoms.
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How time-restricted eating helped my patient shed the pounds in three months
One of the most satisfying cases I’ve had recently was Shilpa, who had been overweight since childhood. Because her family had problems with their weight, she assumed it was in her genes and that there was nothing she could do about it.
She worked as a PA at a law firm and I could tell that she was a naturally organised person who thrived on order, so I asked if she’d heard of time-restricted eating. She immediately liked the sound of it.
We chatted about her eating schedule. She had a one-hour commute and would eat two slices of toast at 6.30am before leaving for the station. She’d get home at 7.30pm and would eat dinner at 8pm. Finally, she’d curl up in front of the telly with a packet of sweets, which would usually last her until 10pm. This made her eating window just over 15 hours.
Initially, I asked her to reduce it to 12. Instead of toast, she would take a couple of boiled eggs into work with her and eat them at 8.30am. She also tried to drop those after-dinner sweets, which she found challenging at first.
However, within days, she felt better. Her sleep quality had improved and she felt lighter and more energetic. She thought that she already slept well, but when she woke up feeling ready to bounce out of bed, she realised how wrong she’d been.
She moved her eating window down to 10 hours, delaying breakfast until her mid-morning break at work. Over the course of a few weeks, she noticed that her IBS-type digestive symptoms had improved significantly as well.
Once Shilpa’s body got used to her eating window, her system adapted and her signals changed so she felt less hungry. She was more productive at work and felt better about herself.
Finding herself much more energetic in the evenings, she joined a martial arts class, which was something she’d always wanted to do but always felt she was too heavy. She took the lessons not to burn calories but because they made her feel good. But guess what? Her weight fell off. Within three months, she was slimmer than she’d ever been in her adult life, and she’d barely made many changes to her diet at all.
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