Altering your metabolism is a lost cause — here's why and what to do instead 

We usually associate our metabolism with activity and age, but a growing body of research finds this is not the case

One study conducted by scientists at the University of Campinas in Brazil, found half of gastric bypass patients regain all the lost weight within just two years

We often succeed in meeting short-term weight goals through diets, but the bleak reality is that about 90% of people who manage to lose significant amounts of weight, ultimately end up putting all of it back on.

Scientists believe the reasons for this are connected to our metabolism, the set of chemical reactions inside our cells which convert the calories in food into the energy our body requires to complete the necessary functions to keep us alive.

According to Dr Daniel McCartney, a lecturer in Human Nutrition and Dietetics at Technological University Dublin, people who embark on crash diets, where they drastically restrict their food intake over a few weeks, tend to shed more muscle mass compared to fat tissue, which takes longer for the body to burn.

McCartney explains that when we deplete our muscle reserves over a short period of time, our metabolism naturally slows down, and the body starts burning through calories more slowly to conserve its resources. 

“The consequence of this is when the diet ends, and you resume normal eating habits, you have a greater propensity not just to gain weight, but more weight than you lost in the first place,” he says.

Part of the problem is that when we gain weight, our body swiftly adapts to the new normal. As a result, even people who opt for weight- loss operations, experience a drop in metabolism, meaning they have to eat significantly less to avoid gaining weight again. 

One study conducted by scientists at the University of Campinas in Brazil, found half of gastric bypass patients regain all the lost weight within just two years.

But scientific research into our metabolism is also offering insights into why we gain weight in the first place, such as the ‘middle-aged spread’ that many of us experience through mid to later life.

Metabolism myth

While it was long accepted that the body’s metabolism begins to slow in early adulthood before continuing to drop for the remainder of our lives, this idea has recently been debunked.

In a landmark 2021 Science paper, Herman Pontzer, an associate professor of evolutionary anthropology at Duke University, North Carolina, and colleagues examined metabolism data from 6,400 people, ranging from newborn babies to nonagenarians. They found that instead of declining, our metabolism stays relatively stable between 20 and 60, even during major hormonal shifts such as pregnancy. 

A 50-year-old woman going through the menopause still burns calories at the same rate as a 20-year-old.

“It’s a change in the conventional wisdom,” says Pontzer. “It changes how we think about how hormonal changes affect our bodies as we age, how activity levels change.”

It also means that we need to look for alternative explanations for why we start to gain weight in our 30s, 40s and beyond. 

Scientists think we have to look more at lifestyle factors rather than simply accepting this change as an inevitable consequence of age.

“People tend to sleep a little bit less from middle adulthood onwards, and that can be a factor,” says McCartney. “We know that less sleep and disrupted sleep patterns are something that also predisposes people to gain weight.”

The other major factor is the availability of cheap, high-fat, high-sugar, and calorific foods

The other major factor is the availability of cheap, high-fat, high-sugar, and calorific foods. McCartney speculates that as we age, the combination of work and life stresses leads many people to consume more calories while becoming progressively more sedentary.

“We talk about the obesogenic environment,” he says. “There are a lot of converging factors that not only predispose us to overconsume these foods but are conspiring to cause us to lead more sedentary lifestyles.”

Body fat and chronic disease

A myth propagated by many fitness programmes is that exercise increases your metabolism, helping you burn calories at a greater rate. 

Pontzer says this link between exercise and weight is false. In 2018, he published a study which showed that indigenous tribes in northern Tanzania who walk up to 19,000 steps a day still burn the same number of overall calories per day as sedentary individuals in Europe and North America.

Pontzer believes that the body is pre-programmed to burn a set number of calories per day relative to our body size, which it needs to maintain our body temperature at the correct level, and keep oxygen moving throughout our cells and tissues.

He says that exercise is still vitally important but in a more subtle way. In keen amateur athletes and regular gym-goers, any excess calories will be diverted towards the muscles to provide them with the fuel they need. 

But, for those who work at a computer and spend their leisure time on Netflix, these excess calories will gradually accumulate around the body over the years as visceral or hidden fat.

This fat is stored deep inside the belly and wrapped around organs like the liver and intestines. Its presence is increasingly thought to be linked to the development of a range of chronic illnesses from cancer to type 2 diabetes and cardiovascular disease, which has brought it to the attention of researchers such as Dr Frederick Sheedy, a biochemist at Trinity College Dublin.

Sheedy says that visceral fat is particularly problematic because it interacts with the immune system by producing a continuous flow of inflammatory molecules. 

“In obese people who have a lot of visceral fat, there’s a constant pressure on the immune system, and that pressure isn’t being released,” he says.

Pontzer says this link between exercise and weight is false

Because so much of the body’s energy is being diverted to generating this low-grade inflammation, Sheedy explains that the immune system has less capacity to fight off external pathogens — which is why overweight people have been more vulnerable to Covid-19 — or to seek out and destroy tumours. 

“For our immune cells to do their normal job, which would be dealing with infections or cancers, they need a lot of energy,” he says. “This is a connection we have overlooked for a long time.”

The inflammatory molecules produced by visceral fat cells also compete with insulin, a hormone which controls our blood sugars and, to some degree, our likelihood of gaining weight. As a result, the presence of inflammation means that the body starts to produce more insulin to keep blood sugar under control. 

“Unfortunately, those high insulin levels also predispose us to gain more fat tissue and weight, creating even more inflammation,” says McCartney. “It becomes a vicious cycle which eventually leads to type 2 diabetes.”

What can we do?

So how do we prevent the slow proliferation of harmful visceral fat over time? It is a challenge that becomes even more pronounced after age 60 when our metabolism begins to decline sharply.

Despite the marketing campaigns of various wellness supplements, attempting to change your metabolism is a lost cause. Even if we could, it is unclear whether it would greatly impact our weight. 

Pontzer points to a 2022 study he co-authored that compared people with genetically fast metabolisms — people who burn more calories per day than would be expected for their body size — to people with genetically slow metabolisms. The study found little connection between metabolism and the propensity for gaining weight.

Instead, he believes it is all about ensuring that we do not consume an excess of highly calorific foods.

“It’s quite hard to change your own individual metabolism,” he says. “All these metabolism-boosting supplements and foods and tricks are all bullshit. 

"So the focus in terms of your weight really has to be on the energy that you’re eating.”

Rather than crash diets, scientists believe the key is structured regimens which are designed to be incorporated into longer-term eating habits, such as intermittent fasting where individuals gradually become accustomed to not eating for a period of time each day or week.

Sheedy is particularly interested in intermittent fasting as a way of shedding visceral fat because the periods of fasting help to relieve pressure from the immune system, allowing the body to process and deal with any inflammation.

Exercising is also crucial because it helps retain muscle tissue, pushing the body to focus on burning fat reserves. 

“Exercise and intake of low-fat dairy foods are both good because they help maintain lean muscle mass,” says McCartney. 

“In terms of your metabolic health, exercise also helps process inflammation, which improves insulin sensitivity, so there’s less likelihood of subsequently gaining weight.”

Early detection of cancer  

In future, our growing understanding of the intricacies of metabolism could also be used to improve our means of detecting signs of chronic disease. Cancer cells can be differentiated from healthy tissue at the cellular level because their energy requirements are so much greater as they seek to proliferate out of control.

Stockholm-based biotech Elypta is now looking to use this information to aid early detection of cancer. The company is currently trialling a system that searches for abnormal quantities of metabolites — substances produced when a cell metabolises the nutrients from food into energy — called glycosaminoglycans, in a saliva or urine sample.

Research into kidney cancer has shown that tumours produce much larger quantities of glycosaminoglycans than healthy cells, meaning that they can be used as cancer biomarkers.

Glycosaminoglycans could form the basis of non-invasive diagnostic tests for a whole range of cancers. “There are standard screening programs for breast or prostate or colorectal cancer for example,” says Francesco Gatto, co-founder of Elypta.

“But there are over 200 different types of cancer. We can’t do screening for every single one of them, that’s impractical. So we need a better way of trying to identify whether there are signs of cancerous cells in the body and we feel we can use metabolism as a source of biomarkers for cancer detection.”