Science rocks. It's by far our best way of understanding reality.
But most of us, me certainly included, often are prone to embracing folk wisdom rather than science when it comes to losing weight.
I'm six feet tall and 178 pounds at the moment -- though sadly, my long-term trend (I'm 72) has been to lose a bit of height and gain a bit of weight.
Since I'd like to get to about 175 pounds and know how difficult it is for me to lose even a few pounds, I was eager to read the front page story in the February 27 New Scientist issue, "Metabolism Myths: Seven Things We Get Wrong About Diet and Exercise."
The author, Herman Pontzer, has impressive credentials. Here's the bio on his Amazon page.
How did the human body evolve, and how does our species' deep past shape our health and physiology today? Through lab and field research, I investigate the physiology of humans and apes to understand how ecology, lifestyle, diet, and evolutionary history affect metabolism and health.
I'm also interested in how ecology and evolution influence musculoskeletal design and physical activity. Field projects focus on small-scale societies, including hunter-gatherers and subsistence farmers, in Africa and South America. Lab research focuses on energetics and metabolism, including respirometry and doubly labeled water methods.
(He's written a recently released book, Burn: New Science Reveals How Metabolism Shapes Your Body, Health, and Longevity.)
These are the Seven Metabolism Myths in the New Scientist story, along with excerpts. Some surprised me. Some didn't. Bottom line: if you want to lose weight, likely you've got to reduce calories. There's no short cut.
Remember: the boldfaced headlines are myths.
(1) Exercise burns through calories and boosts metabolism. It is the bedrock belief of pretty much every workout routine featured in magazines: exercise more, burn more calories. In the short term, it is correct – you burn energy while you are exercising, and if you start a new workout routine, you will burn more calories, at least in the beginning. But recent studies show just how dynamic and adaptive our metabolisms can be.
...Daily expenditures measured for participants in exercise studies routinely increase at the beginning of a new workout regimen, but those gains diminish over time. Their bodies adapt, so that within a few months, the daily energy they burn is only marginally higher, and sometimes exactly the same, as before they started working out. The boost is a bust.
(2) Exercise will make you lose weight. Even those who do manage to increase the amount of energy they burn through exercise typically still find it hard to lose weight. A recent review of 61 exercise studies, totalling more than 900 participants, lays out the grim evidence that will be familiar to many.
Weight loss often starts off well at the beginning of a new exercise regime, but it fades over time, so that a year or so later, the weight lost is a vanishing fraction of what we would expect from all the calories burned through working out.
...The reason for this is frustratingly simple: when you burn more calories, you eat more calories. You might not mean to, of course, but that is the problem. The complex systems working subconsciously to regulate your hunger and satiety do an exceptional job of matching energy intake to expenditure.
(3) Your workout programme isn't succeeding unless you are losing weight. Not losing weight? Don’t give up! Exercise might not change the number on your bathroom scales, but that isn’t what it is for. Humans evolved as hunter-gatherers, and a heavy dose of physical activity was an inescapable part of the daily routine for more than 2 million years.
Our bodies are built to move, and there are good reasons why the Hadza avoid heart disease and diabetes, despite the fact that they burn the same amount of calories as sedentary people. Regular exercise keeps our hearts healthy, our muscles strong and our minds sharp, especially as we age.
Intriguingly, recent studies suggest that the metabolic adjustments that frustrate weight loss are a big reason why exercise is so good for us. My lab and others are working to track down the precise nature of these changes, but it seems our bodies respond to increased daily activity by reducing the energy expended on other tasks.
(4) Calories don't matter. Gaining weight is fundamentally a physics problem: when we eat more calories than we burn, those extra calories pile up as fat. Since it is futile trying to boost the energy we burn each day with exercise (or superfoods, or ice water, or the latest gimmick), the primary cause of being overweight or obese is clearly diet. We gain weight because we eat too much.
Yet counting calories has become passé. We are told it is the types of foods we eat, or the way that we eat them, that get us into trouble, and that the “calories in, calories out” view of the world is for suckers. Low-carb evangelists tout ketogenic diets – which rely heavily on fat, rather than carbohydrates – as a way to lose weight without cutting calories (some even claim you can eat more). Intermittent fasting fanatics promise much the same.
...If you are attempting to lose weight, the trick is to find a diet that you can maintain without feeling miserable. Foods high in protein and fibre tend to make us feel full. It also helps to avoid crash diets that can cause our clever, evolved metabolisms to hit the brakes and reduce daily energy expenditure.
(5) Humans evolved to eat a Paleo diet. Striving to eat the kinds of foods our ancestors ate makes intuitive sense. But emulating ancient diets, the idea behind the fashionable Paleo or “caveman” diet movement, in which people eat similarly to how our ancestors did in the Palaeolithic era, isn’t as straightforward as it might appear.
Cast your mind across the dizzying array of cultures on this planet, and consider the staggering variety of foods we eat. Clearly, there is no single human diet today, and it would be laughable to claim otherwise.
...Hunter-gatherer diets are (and were) just as diverse as diets in industrialised populations, with lots of variety among groups and through time in the proportions of meat and plants, fat and carbs. Some diets, particularly those of Indigenous people in the Arctic, are meat-heavy; others, especially in warmer climates, are plant-heavy.
(6) A slow metabolism dooms you to obesity. Like most other biological traits, the amount of energy burned in a day varies from person to person. Daily energy expenditure in two people who are the same age and sex, and have the same lifestyle, can easily differ by 500 calories or more. Surprisingly, that variation in energy use doesn’t predict someone’s weight.
People with obesity have the same daily energy expenditure, on average, as those who are slim. That’s after accounting for body size, since a larger body tends to burn more calories per day simply by virtue of having more cells at work. If we don’t correct for size, people with obesity burn more energy. Weight gain and obesity aren’t products of a slow metabolism.
So why do some people find it easy to stay trim while others struggle? Although there is probably no single answer, a major factor seems to be the way our brains are wired. For most, weight gain comes on slowly over months and years, reflecting tiny errors in the regulation of energy intake.
The vast array of processed and engineered foods available to us overwhelms neural reward systems evolved to handle unprocessed wild foods. Our brains err on the side of overconsumption.
(7) Obesity and weight gain are a sign of personal failure. As powerful as our genes are, DNA isn’t destiny. Today’s gene pool is essentially unchanged from that of our great grandparents’ generation because genetic change is slow. They didn’t face a global obesity crisis. What’s different in much of the world is our environment, specifically our food environment – the access we have to specific foods.
In engineering our industrialised world, we have surrounded ourselves with foods that drive us to overconsume. The battle with obesity is often framed as a test of willpower, pitting the virtues of exercise and portion control against the vices of gluttony and sloth. New metabolic science says otherwise. Shops are stocked with ultra-processed foods, laden with added sugars and oils, symphonies of sweet and savoury that overwhelm our Palaeolithic brains.
...In wealthy countries, ultra-processed options often dominate the foods available in low-income neighbourhoods and those where the majority of inhabitants are from minority groups, contributing to inequities in health and nutrition. In low and middle-income countries, the growing dependence on ultra-processed foods has helped to fuel the global rise of obesity and related disease.
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