Photo / Towfiqu Barbhuiya, Unsplash
There is a new buzz-phrase being touted as the way to ditch the midlife extra pounds, as well as prevent chronic disease like Type 2 diabetes, without the need for a depressing diet regime.
Forget soups, shakes and a life of no carbs - instead, experts say, we need to retrain our bodies to return to a more natural metabolic flexible state.
"Metabolic flexibility is how well your body can switch between using carbohydrates and fats for energy," explains registered nutritionist Rhian Stephenson, founder of wellbeing business Artah.
"Our bodies are designed to do this seamlessly so that we can maintain energy production in times of caloric restriction, such as when we had to hunt for food, or increased energy demands."
The body naturally burns carbohydrates first because they are easier to convert to energy – but if we can retrain the body to burn both more readily, it boosts the ability to lose weight.
But our modern diet and lifestyle can often impair this essential process, which can lead to metabolic imbalance and disease.
According to a paper in Endocrine Reviews: "Disrupted metabolic flexibility is associated with many pathological conditions including metabolic syndrome, Type 2 diabetes mellitus and cancer."
One in three midlifers over the age of 50 will suffer from metabolic syndrome, a combination of diabetes, high blood pressure (hypertension) and obesity, according to the NHS.
It largely comes down to what we eat. "The quality of our food is a big factor that makes us inflexible," Stephenson says. "The main contributor to this loss of flexibility is impaired glucose metabolism and hyperinsulinemia, or too much insulin. When our diets are too high in refined processed foods, refined carbohydrates and sugar, we are constantly spiking insulin and using sugar as our primary source of fuel."
We also eat too often. "When you think about our trained eating habits – three meals a day plus snacks – it's not reflective of our body's natural rhythm or how we're designed to burn energy," Stephenson says.
Despite these healthy eating guidelines, not all of us will respond to food in the same way. That's where a raft of new tech comes in, fuelling our interest in personalised nutrition with devices from blood glucose monitors to CO2 trackers to metabolism trackers that aim to give us in-depth data on how foods are affecting our body.
"There is a marked sea change in the way we think about nutrition now," says Professor Tim Spector, author of Spoon-Fed, Why Almost Everything We've Been Told About Food is Wrong. "It's not just about calories in, calories out; it's the way your body reacts to food on a very individual level."
In fact, according to Predict, the largest in-depth nutrition study in the world, there is "up to a tenfold variation in responses to the same meal for different people".
One handheld smart device I have trialled is Lumen, which measures your metabolism in real-time using the CO2 in your breath. To train it, you have to breathe into it after waking, before eating, after eating, before exercise, after exercise, before sleep: as the device learns more about you, it works out when you are burning carbs or fat and suggests nutrition plans based on the number of macro nutrients (carb, fat and protein) to get into the fat-burning zone.
But unlike a standard keto diet, which condemns you to a life of no bread, over time the plans adjust, introducing high carb days to keep your metabolism on its toes, thereby improving its flexibility.
"We promote a dynamic low carb approach to nutrition, with gradual high carb days to make sure your body is burning fats and carbs according to your energy expenditure," says Michal Mor, co-founder and head of science at Lumen.
"Low carb days decrease the insulin spike, improving insulin sensitivity, and deplete your body's carb stores, enhancing mitochondrial function. High carb days ensure your body's ability to use carbs for energy and keep hormones in balance."
After two weeks of using Lumen, I could see what high carb meals and snacks were doing to my metabolism: pushing it back into carb-burning zone. It showed me that an evening meal that was carb-heavy – pasta, for example – had an effect on my ability the next morning to burn fat.
It was also gratifying to see that delaying breakfast gave my metabolic flexibility a boost. Breathing into the device and hoping for a low score – indicating fat-burning – became like a game.
Other metabolism-boosting tricks it recommends cross over with Spector's findings, too, such as intermittent fasting or time-restricted eating which, Mor says, "depletes your body's carb stores, which in turn enhances mitochondrial function to burn more fat and increase insulin sensitivity".
But even fasting is personal: according to Lumen's data, 27 per cent of people who fasted for more than 10 hours stressed their body, resulting in carb burn, rather than fat burn.
I haven't used it long enough to see dramatic results, but Maria Fox, 51, a police superintendent, credits Lumen with re-educating her about nutrition and hacking her metabolism, leading to a loss of about 20kg in weight.
It is not the only high tech approach; along with continuous blood glucose monitors, which are particularly popular in America, with tech companies including Levels, NutriSense and January, there is ZOE, an AI-powered nutrition programme co-founded by Spector that requires users to test gut, blood fat and blood sugar responses with an at-home kit, before the results are analysed in a laboratory and a personalised report is sent back.
"To reduce the metabolic stress in your body, and therefore reduce the inflammation, you have to adjust the food you eat," Spector says. "But it can vary wildly between people. I used to eat brown toast and muesli for breakfast, but I found through testing that was terrible for me, so I've switched to yogurt with nuts and seeds. My wife can have as much bread as she wants, which is very annoying."
ZOE, which has so far only been available in the US, has found that along with losing weight, 57 per cent of programme followers report the eating plans have given them more energy, with 88 per cent saying they do not feel hungry. The programme, which has undergone three independent research studies since 2018 as well as an ongoing 800,000-person clinical trial, will be launched in the UK before their summer.
Spector, an epidemiologist at King's College London, is slightly sceptical about some of the tech products on offer, but agrees that "they help provide an awareness of" personalised nutrition and the need for a flexible metabolism.
Of course, you can boost your metabolic flexibility without the tech. "Unravelling habits is entirely possible, and the process gets easier as the quality of your diet and efficiency of your metabolism improve," Stephenson says.
It means looking at the quality of your food, eliminating sugar and alcohol along with snacking. For those who need support, she is running a five-day "Virtual Recharge" with meal plans and nutritional check-ins, plus daily exercise to help boost metabolic flexibility and "deliver a body reboot".
According to a paper published in Cell Metabolism, "Exercise profoundly affects metabolic flexibility". But while we may have been caught up on which type of exercise (high intensity or low impact, for example) is better for fat-burning, David Higgins, author of The Hollywood Body Plan: 21 Minutes for 21 Days to Transform Your Body For Life, and trainer at the studio Movementum, says: "Increasing your movement in any way will contribute to your metabolic flexibility. Focus on things that increase your body's natural resting heart rate, whether that's jobs around the house, or a long walk." But the main thing is to do your exercise in a fasted state, he says.
Changing our metabolism is possible, but it takes work. For Stephenson, the key is not to see this as another "quick fix". Instead, she says, this is a "long term solution for health, because that is what really counts".
• Fast. Try to allow at least 12-14 hours between your evening meal and breakfast to give your gut a break and deplete your carb stores.
• Exercise first thing. Do your cardio – be it a walk or a gym session – in a fasted state to burn more fat.
• Ditch the snacks. Give your metabolism a break and stick to eating at mealtimes. It will also prevent you from over-eating.
• Increase the plants. Spector recommends aiming for up to 30 plants each week, including spices, herbs, nuts, and seeds.
• Go low carb. "This is the highway to getting your body to use up your carb stores so you can then shift to burning fat," according to Mor.
The new free open-air saltwater pool is already proving popular.