Prof Herman Pontzer<\/a> \u2013 one of the 68 scientists behind the new research.<\/p>\nSo, is it time we all chuck out our running shoes and cancel gym memberships? Spoiler: sadly not. While this research suggests \u2018how much you move\u2019 has very little bearing on \u2018how much you weigh\u2019, giving up on exercise isn’t the answer either.<\/p>\n
Metabolism myths<\/p>\n
If, as the new study suggests, only a sliver of your daily calorie burn comes from exercise, what\u2019s using up the rest? In short: everything your body does behind the scenes to keep you alive.<\/p>\n
Your lungs drawing in air, your heart pumping blood, your immune system fighting infections, your gut digesting food, your brain firing with thoughts \u2013 all of these processes need energy. A lot of it. In fact, this background work, known as your basal metabolic rate (BMR), accounts for the overwhelming majority of calories you use each day.<\/p>\n
![\"Cross-section](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/01\/kidneys.jpg\")
Though they make up less than 1 per cent of your body weight, your kidneys use about 10 per cent of your energy. Photo credit: Getty<\/p>\n
And here\u2019s the crucial point: the more cells and mass you have, the more energy you\u2019ll need overall, and the larger your basal metabolic rate will be. It makes sense in theory, but the real-world results are pretty surprising.<\/p>\n
Namely, thanks to their larger size, the overweight US office worker will generally have a higher basal metabolic rate than the Hadza hunter-gatherer.<\/p>\n
\u201cPeople in the developed world burn more calories every day than people in farming, foraging and traditional groups,\u201d Pontzer says. \u201cThey burn more, because people in the developed world tend to be bigger, and being larger generally means you\u2019re going to burn more calories.\u201d<\/p>\n
It all means that once you account for body size and composition, there\u2019s \u201chardly any difference\u201d in total energy use between populations around the world, says Pontzer, referring to the study.<\/p>\n
Or, to put another way, pound-for-pound, the office worker tied to their desk will use a similar number of calories per day as somebody far more active.\u00a0<\/p>\n
The calorie equation<\/p>\n
How could it possibly be that we all burn about the same amount of energy for our body size? According to Pontzer, it\u2019s because when we move more (or less), our bodies don\u2019t simply burn extra calories; our metabolism adapts, conserving energy elsewhere to balance things out.<\/p>\n
Simply put, our bodies want to stay in balance (a process biologists call homeostasis). This means that, Pontzer says, if you suddenly decided to cartwheel across a meadow every morning, your body would adapt, shifting its energy resources away from some of those background tasks to accommodate your new exercise habit.<\/p>\n
\u201cOur bodies are able to adjust to our different lifestyles,\u201d he explains. \u201cIf we\u2019re more physically active, our bodies seem to adjust to spend less energy on other stuff. The total calories burned per day is not different, even though we\u2019re more or less physically active.\u201d<\/p>\n
Spending fewer calories on other bodily functions may sound alarming, but Pontzer says it\u2019s usually not something to worry about \u2013 in fact, it\u2019s desirable.<\/p>\n
\u201cRejuggling how calories are spent is a really good thing. Most of us spend excess calories on things like background inflammation,\u201d he says.<\/p>\n
By redirecting energy away from those unnecessary background processes, exercise helps the body run more efficiently \u2013 reducing inflammation and keeping us healthier overall. In this way, Pontzer says that while it might not be the key to shedding weight, it\u2019s crucial for maintaining a healthy, balanced body.<\/p>\n
![\"Smiling](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/01\/running-man.jpg\")
A 5K might feel like extra calories burned, but your metabolism quietly balances the books. Photo credit: Getty<\/p>\n
Of course, this effect only goes so far. Suddenly ramping up your activity levels can put strain on your body, causing your immune or reproductive systems to take a hit. You might find yourself getting ill more often, your libido dropping, or your periods stopping altogether.<\/p>\n
\u201cIt\u2019s called overtraining syndrome,\u201d says Pontzer. \u201cBut, unless you\u2019re a professional-level athlete, you\u2019re probably not going to see that.\u201d<\/p>\n
The same thing happens in reverse when you suddenly stop exercising. If you give up your cartwheeling, for instance, your metabolism shifts gears \u2013 redirecting that spare energy into background processes like inflammation instead.<\/p>\n
\u201cRegardless of how active you are, the body adapts dynamically to keep expenditures within a narrow range,\u201d explains Pontzer.<\/p>\n
The foods that fuel fat<\/p>\n
In short, according to Pontzer, the real factor associated with body fat percentage isn\u2019t exercise \u2013 it\u2019s food.<\/p>\n
\u201cAll the weight that we carry is the calories that we ate and never burned off,\u201d Pontzer says. \u201cAnd so, if our energy expenditures aren\u2019t different, then it must be diet.\u201d<\/p>\n
However, the researchers found that one type of food stood out as the main culprit behind weight gain. It wasn\u2019t how much meat or other main food groups people ate that explained differences in obesity \u2013 it was the amount of ultra-processed food in their diets.<\/p>\n
These packaged products are made in factories, using industrial ingredients and techniques, and sold in shops. They might include supermarket bread, biscuits, sweets, snacks, colourful cereal, bottled sauces, ready meals, flavoured yoghurts \u2013 and more.<\/p>\n
![\"Ultra-processed](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/01\/jelly-bean.jpg\")
Ultra-processed foods make up about 60 per cent of the average American diet. Photo credit: Getty<\/p>\n
\u201cWhat we saw is that, sure enough, across all these groups, the amount of ultra-processed food that these populations are eating is a good predictor of how much body fat they have,\u201d says Pontzer. <\/p>\n
\u201cIt\u2019s correlational, but I think it\u2019s very suggestive that if you eat more ultra-processed food, you\u2019re more likely to be overweight and obese.\u201d<\/p>\n
While the findings are compelling, it\u2019s important to note that the researchers didn\u2019t directly measure what participants ate. There were no food diaries, calorie logs or nutrient breakdowns for either the US office workers or the Hadza members. Instead, the team drew on population-level data from national dietary surveys and global food consumption databases to estimate participants’ typical diets.<\/p>\n
That might sound like nitpicking, but it\u2019s a crucial limitation. Because we can\u2019t see the link between ultra-processed foods, body fat and energy expenditure on an individual level, we can\u2019t be sure why ultra-processed foods may lead to obesity.<\/p>\n
It could be that, calorie for calorie, ultra-processed foods have particularly harmful effects. Or \u2013 as Dr Adam Collins<\/a>, associate professor of nutrition at the University of Surrey, argues \u2013 it might simply be that these foods make it far easier to overconsume calories.\u00a0<\/p>\n\u201cIt\u2019s not the ultra-processing itself,\u201d he says. \u201cIt\u2019s the properties of these foods that make them hyper-palatable, easy to overconsume \u2013 as well as the fact that they\u2019re usually energy dense but not very nutritionally dense.\u201d<\/p>\n
![\"Most](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/01\/UPF-bread.jpg\")
Most supermarket bread counts as an ultra-processed food, thanks to the additives and emulsifiers that keep it soft and shelf-stable. Photo credit: Getty<\/p>\n
By definition, ultra-processed foods are designed to be as delicious as possible, which means they tend to be high in salt, fat and sugar, low in fibre and nutrients, and easy to eat quickly and in large portions.<\/p>\n
\u201cWhen people say they\u2019re going to cut out all their ultra-processed food, what happens?\u201d says Collins. \u201cPeople end up eating less. People are more mindful of what they\u2019re eating. They end up losing weight and becoming healthier.\u201d\u00a0<\/p>\n
He adds: \u201cIt’s not that we’ve got to cut out all ultra-processed foods, or that every ultra-processed food is bad.\u201d Instead, we might benefit from consuming them more mindfully and in moderation.<\/p>\n
Chewing the fat<\/p>\n
The new study, however, isn\u2019t without its critics \u2013 Collins among them. In particular, he argues that exercise does play more of a role in weight loss than it\u2019s given credit for.<\/p>\n
\u201cIt\u2019s true that exercise might not burn off many calories directly. And tracking \u2018calories in versus calories out\u2019 \u2013 this thinking of \u2018I\u2019ll just run off that chocolate bar\u2019 \u2013 is outdated,\u201d he says.<\/p>\n
\u201cBut exercise can help regulate appetite and change body composition, reducing body fat and increasing muscle mass.\u201d<\/p>\n
As Collins points out, muscle cells are more metabolically active than fat cells, meaning that building more muscle subtly raises your daily energy needs and overall calorie burn.<\/p>\n
![\"Woman](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/01\/smart-watch.jpg\")
Your smartwatch might say you\u2019ve \u2018burned off\u2019 that snack, but according to Pontzer, your body simply burns less elsewhere to stay in balance. Photo credit: Getty<\/p>\n
Pontzer agrees that exercise can change body composition, which in turn affects metabolism \u2013 but he says these are \u201creally small, marginal changes,\u201d and that exercise programmes relying on them for weight loss generally don\u2019t work.<\/p>\n
Collins, however, remains unconvinced. He calls Pontzer\u2019s model \u201ca neat idea,\u201d but says it\u2019s still unproven \u2013 and that long-term studies following individuals over their lifetimes are needed to truly test it.<\/p>\n
Why you still need exercise<\/p>\n
Despite disagreements over how effective exercise is for fat loss, one thing everyone agrees on is that it\u2019s incredibly good for us. It strengthens the heart, protects bones, keeps metabolism in check and boosts mental wellbeing \u2013 helping us live longer, healthier lives.<\/p>\n
Pontzer is hoping that health advice about weight will change \u2013 but he\u2019s not advocating that people abandon exercise.<\/p>\n
\u201cRather than blaming both diet and physical activity equally, which is how it\u2019s all framed right now, I hope that we can focus entirely on diet for the obesity crisis, because that seems to be the main driver here,\u201d he says.<\/p>\n
\u201cIt doesn\u2019t mean that we should stop exercising or stop telling people to exercise. Those are important goals as well \u2013 but we really need to focus our efforts on diet.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"If you want to lose weight, exercise doesn\u2019t really matter. That doesn\u2019t sound right, does it? After all,…\n","protected":false},"author":2,"featured_media":212104,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[37],"tags":[565,134,111,139,69],"class_list":{"0":"post-212103","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-fitness","8":"tag-fitness","9":"tag-health","10":"tag-new-zealand","11":"tag-newzealand","12":"tag-nz"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/212103","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=212103"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/212103\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/212104"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=212103"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=212103"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=212103"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"Hadzabe](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/01\/hazda.jpg\")
The Hadza of Tanzania often walk 8 to 16 kilometres (5 to 10 miles) a day while hunting and foraging \u2013 about the same distance most of us cover in a week. Credit: Getty<\/p>\n