Burn, baby, burn: the new science of metabolism

Susan Roberts, director of Tufts University's Energy Metabolism Laboratory, Massachusetts, has spent the last two decades researching ways to combat the obesity epidemic that continues plague many parts of the west.
Roberts and other experts in obesity have been confronted with this problem repeatedly. Although it is easy to get overweight people to lose weight, it is more difficult to prevent them from gaining their lost weight.

According to the University of Michigan about 90% of people who have lost significant weight through diets, structured programs, or drastic measures such as gastric surgery are able to regain it.

This is why? Scientists believe the reason lies in our metabolism. This complex series of chemical reactions in cells converts calories into energy that our bodies require to breathe, maintain organ function, and keep us alive.

We know that when someone starts a new diet, their metabolism drops. This is because they are suddenly eating fewer calories. The body then burns them slower, possibly an evolutionary response to avoid starvation. But what happens over the next weeks, months and years is less clear.

Roberts asks, Does metabolism keep going down more than it should? Or does it start to decline and then rebound? This is a controversial topic that we wanted to tackle.

Our metabolism seems to be almost stable between the ages 20 and 60, even when there are major hormonal changes

We may find some answers over the next three- to four year. Roberts will be leading a study funded by the National Institutes of Health USA. It will follow 100 people over many months as they lose weight and then gain weight. The study will measure everything, from energy expenditure to changes to blood, brain, and muscle physiology to see what happens.

These implications could have huge consequences for how we deal with obesity. It could be that diets cause innate biological changes in our bodies that eventually lead to us eating more. If the metabolism continues to drop and stays low while we lose weight, this could indicate that it is a sign that dieting causes our metabolism to drop. If the metabolism returns to normal, it could indicate that weight gain is due to a recurrence or cultural factors encouraging us to eat more.

Research consistently shows that losing excess weight is more difficult than losing it. But metabolism is the key. Photograph by Peter Dazeley/Getty Images

Roberts says that if someone's metabolism drops and doesn't recover after weight loss, then it means we need to spend all our money on prevention. You are doomed once it happens. The metabolism may rebound, which means that you have learned the hard way not to eat less because your body is smaller. People who have lost weight might be encouraged to consult psychologists about habit formation. These are so many different conclusions, that it is essential to make the right decision.

This is only one example of the many ways that our understanding of metabolism is changing. Many of the old assumptions that exercise can increase metabolism have been challenged in recent years. They also suggested that metabolism will decline as you get older. These answers could change many aspects in public health, according to scientists who are at the forefront of this field.

The age myth

A paper in Science published in mid-August challenged one of the universal truths about metabolism. Scientists have known for decades that middle-aged spread is a phenomenon that occurs when metabolism slows down in young adulthood.

This may be false. The data compiled by Herman Pontzer (an associate professor of evolutionary Anthropology at Duke University in North Carolina) and more than 80 other scientists over the past several years shows that something quite different.

Our metabolism seems to be almost constant between 20 and 60, even when there are major hormonal changes like pregnancy and menopause. According to the latest data, a woman aged 50 will burn calories as efficiently as a woman aged 20.

If our daily calories remain largely the same throughout life, then the true source of obesity must be how much we eat.

There are only two major life changes in metabolism that occur between the ages of one and fifteen months. According to Science, infants use energy at a faster rate than adults in order to support their development. Their metabolism is over 50% higher at one year of age than that of adults. At 60, our metabolism starts to decline again and continues to do so until death.

Pontzer says that for a lot of your life your body is just chugging along on the same trajectory as how busy your cells will be. It is very difficult to change the course of your cells.

What does this all mean? What does this mean? Pontzer claims that obesity is caused by the way we eat, especially if our daily calories remain the same throughout our lives.

One of the most popular marketing strategies used to promote various exercise programs and wellness supplements over the years has been the claim that they increase your metabolism. Pontzer claims that this is almost all nonsense.

Research that compared northern Tanzanian hunter-gatherers who average 19,000 steps per day to sedentary people in Europe and America found that they burned nearly the same amount of calories. Similar results have been found in other studies that examined whether metabolism changes when you exercise or compare non-human primates who live in the rainforest or zoo.

Scientists believe this is because the body has a set amount of energy that it must use each day. Although there may be fluctuations in the day, the body burns the same amount of calories all year. However, it adapts to how we live our lives. Pontzer uses the example of an amateur cyclist who rides 100km on weekends to illustrate the concept. While that person will still burn less calories than a sedentary person on average, their energy expenditure will be more geared towards fueling the muscles. While the sedentary person will still burn similar calories, it will be affected by background bodily functions that we don't notice, such as stress and inflammation.

An avid cyclist might not be burning as many calories as they think. Photograph by Compassionate Eye Foundation/David Oakberry/Getty Images

Pontzer believes there is an evolutionary reason for this. While it would be great to burn more energy than you consume in an industrialized world, this is a poor strategy for the wild. There is more food than we evolved to expect. But, the reason why we are gaining weight is that there are modern industrialized foods that are designed to be over-eating. This is the perfect storm to make people obese.

These new discoveries on metabolism have implications for medicine and the way we treat obesity. Because metabolism slows down after 60 years of age, doctors need to determine if older patients should be given slightly different dosages of medicine. The research will also raise questions about the relationship between slower metabolism and the development of chronic diseases in older people.

Individual differences

The Science paper showed general trends in metabolism across all ages. However, we don't know much about individual differences and what they could mean. Are babies born with a rapid metabolism more likely to develop faster and better? Do they develop a slower metabolism due to the different environments they live in, such as social deprivation?

Although this is speculation at the moment, scientists know that metabolism still varies from person to person, even when you take into account factors like body size and composition. Although we don't know why this happens, there are many factors that could be responsible, including genetics, organ size, immune system and the type of bacteria found in the gut microbiome.

It is difficult to keep track of your own metabolism rate even with the most recent digital technology. Pontzer explains that this is because no app on the market today can account for individual differences at resting metabolic rates.

Herman Pontzer and colleagues published research this summer that showed that our metabolism does not slow down. This is true from the earliest years of adulthood until the age 60. Photograph: Huffines Institute

One of the most important questions is whether these genetic variations can increase susceptibility to diseases, particularly those related to metabolic dysfunction like type 2 diabetes and cancer. Eric Ravussin is the director of the Nutrition Obesity Research Center at Pennington Biomedical Research Centre, Baton Rouge, Louisiana. Your diet and weight are key factors. You are more likely to develop hypertension if you gain weight. Inflammation is also more common if you gain weight.

Many startups are exploring ways to use our metabolic knowledge to help develop personalised treatment programs. Dysfunctions in the microbiome of the gut are linked to a variety of metabolic diseases. This is because they play a critical role in energy metabolism by breaking down food.

Bio-Me, an Oslo-based company, is currently profiling the microbiomes in patients with type 2 diabetes and coeliac disease. It uses DNA sequencing to determine the specific species of bacteria found in their intestines. The information can be compared with the existing microbiome data from that patient group, which is available in population biobanks. This information can then be used to predict the dietary or treatment regimens that might be most beneficial for that individual.

Morten Isaksen, CEO of Bio-Me, says this can be used for predicting whether common medications such as metformin will work well in a particular patient. According to Isaksen, metformin works only because the active ingredient in the medicine is converted by the bacteria in the gut. The medicine will not work if there isn't the right bacteria in your gut. Knowing which bacteria is present is crucial for finding the best treatment.

Dysfunctional cell metabolism is key to cancer. It determines how tumors form and how they spread. Early diagnosis of certain types of cancer could be made possible by identifying metabolic dysfunction. Elypta, a Stockholm-based biotech company, is currently testing a system that detects small molecules (known as metabolites) produced by kidney cancer cells. This could one day be used in liquid biopsy to diagnose the disease.

Francesco Gatto (co-founder of Elypta) says that once cancer cells start to multiply, the real change is in their metabolic needs compared to healthy cells. We believe we can use this layer, which is derived from metabolism, in order to identify multiple types early and non-invasively.

Pontzer plans to continue the Science study and explore the extremes in metabolism, both young and old. He says that we will be looking at this variability in both very young children as well as the elderly. We are interested in understanding if people's metabolisms change more rapidly or less than others. Does this predict their health and how they develop their bodies? Maybe it is not. We are going to attempt to discover these things.