A Different Perspective on “Hunter Gatherer Energetics and Human Obesity”
Last week in the media there was a flurry of reports about a study which, they claimed, to be proof that exercise isn’t necessary for weight loss. The study, Hunter Gatherer Energetics and Human Obesity, according to its authors is one of the first of it’s kind to examine energy expenditure in an African hunter-gatherer tribe and compare it with people from a more “modern” sedentary society 1.
The study’s intent was to shed light on our ancestors’ energy expenditure patternsin order to make more informed assumptions about our own bodies’ makeup and needs. They found that sedentary beings in the West burn just as many calories as the hunter gatherers do 1. But how can that be?
BBC News: A study of the Hadza tribe…suggests the amount of calories we need is a fixed human characteristic …The (researchers) found physical activity levels were much higher in the Hadza men and women, but when corrected for size and weight, their metabolic rate was no different to that of Westerners 2.
New York Times: It’s long been believed that a hunter-gatherer lifestyle involves considerable physical activity and therefore burns many calories, far more than are incinerated by your average American office worker each day. And it was true, the scientists determined, that the Hadza people in general moved more than many Americans do… But it was not true that they were burning far more calories. In fact, the scientists calculated, the Hadza’s average metabolic rate, or the number of calories that they were burning over the course of a day, was about the same as the average metabolic rate for Westerners 3.
The media incorrectly concluded that if we burn the same number of calories as these hunter gatherers even though we move less than them, exercise must not be an important factor in Calorie burn and metabolism as had been thought. Some took it a step farther to say that exercise, therefore, must be useless for increasing calorie burn and assisting with weight loss.
Science Daily: These findings upend the long-held assumption that our hunter-gatherer ancestors expended more energy than modern populations…this in turn supports the view that the current rise in obesity is due to increased food consumption, not decreased energy expenditure 4.
BBC News: (The study) suggests the amount of calories we need is a fixed human characteristic…this suggests Westerners are growing obese through over-eating rather than having inactive lifestyles 2…
Not only do these conclusions fly in the face of more than 20 years of research on exercise and Calorie burn, this is a dangerous path to take with a public who desperately needs consistent and responsible guidance regarding how to lose weight and live a healthy lifestyle.
I’ve been asked by clients and students to comment on this media flurry, so here’s what I have to say about it.
First and foremost, from basic physics we know that energy spent moving an object is directly proportional to the object’s mass.
When I spoke about this to Dr. Rosemary Lindle, Professor of Exercise Physiology at the University of Maryland, she put it in very simple terms. “The caloric expenditure of any weight bearing exercise (walking, climbing stairs, jogging, etc) is dependent upon body weight. It takes energy to move body fat, too.
A heavier person will use more calories to perform the same amount of work as a lighter person. So, to compare the groups, you need to relate their energy expenditure to their body weight.”
Let’s say the heavier person and the lighter person both walk 40 meters. The heavier person will burn more calories doing it, because they’re carrying more weight. So, if both groups did the same amount of movement, the heavier people burn more Calories overall.
This study specifically says that the Hadza tribe has smaller builds (by about 50%) than the average westerner including lower body fat percentages. Based on their comparative size alone, it would be expected for them to have a smaller energy expenditure than their Western counterparts (by about 50% – proportionally to the mass difference). However, they have been observed to have very similar energy expenditure to the Westerners – which can only be explained by their higher activity levels.
The hunter gatherers expended 52 Calories per kilogram of body weight per day while the Westerners spent only 37 Calories per kilogram of body weight per day on average.
The media should have emphasized the fact that even though they’re smaller, the Calorie burn per kilogram of weight is higher in the Hadza tribe. This can only be because they’re more active and they have more fat-free mass.
Second, the media should have highlighted the fact that these hunter-gatherers don’t have as active a lifestyle as we may have thought. I don’t know about you, but when I think about hunter gatherers for some reason I think of people running with spears across miles of tundra, and women carrying water on their heads and babies on their backs over hills and streams. I’m willing to bet that the press was banking on all of us thinking this way. But guess what? These tribespeople are smarter than that.
The tribe’s energy burn came from walking an average of 5 miles per day, which is much less than I would have guessed (obviously). How about you? The men hike away from the camp and most likely sit and wait for the opportune time to throw a spear. But of course – they don’t run after the animals across hill and valley! Come to think of it, that would be really silly. The women gather. That means they walk around and forage for food. I’m sure they go for water but they aren’t traveling 12 miles to get it. These are interesting facts found by the study that the media chose to ignore in exchange for diminishing our enthusiasm for exercise.
In addition, the “Westerners” referred to in this study were not all sedentary office workers as the media would like us think. They were participants from other studies that lived in the US and Europe and sometimes even Siberia. Many of these people lead a much more active lifestyle than the average office worker. So the difference between the two groups and how much they move wasn’t as great as it would seem.
The spread of energy expenditure amongst Westerners is considerable – Many European countries and some US urban centers rely on walking and public transport as their primary mode of transportation. For example, a 30 minute walking commute to and from work is quite typical for San Francisco. Similarly, a 30 to 45 minute bike ride to and from work is considered normal in Holland.
1 mile = 2000 average steps (range 1900-2400)
1 block = 200 average steps therefore 10 blocks is a mile
5 miles = 50 blocks or 100 minutes
At a 20 minute mile pace, that’s about an hour and forty minutes of walking per day which is an average commute for some. 5,6
This study in fact, shows there is less of a gap between the amount of exercise done by modern westerners and today’s hunter gatherer than we probably thought. Not that we can sit as much as we like and not have to worry about it, which is what the media would have us believe.
The researchers for the study do not conclude that we all have the same metabolism whether we move more or not like the media wants us to believe.
“The proximate cause of weight gain is energy imbalance, with food energy intake (kCal/day) exceeding total energy expenditure. Our results indicate that active, “traditional” lifestyles may not protect against obesity if diets change to promote increased caloric consumption…
Efforts to supplement diets of healthy populations in developing regions must avoid inundating these individuals with highly-processed, energy-dense but nutrient-poor foods. Since energy output in these populations is unlikely to burn the extra calories provided, such efforts may unintentionally increase the incidence of excess adiposity and associated metabolic complications such as insulin resistance. Indeed, processed, energy-dense foods have been linked to insulin resistance and cardiovascular disease among Australian foragers transitioning to village life 1“.
Because, true to what we have known for some time – if caloric consumption is over and above our needs, our weight and risk for disease increases.
For those struggling to find truth in this mass media mess, here is what we know and still stands true today:
The question is not whether we should diet OR exercise.
We always need to do BOTH.
Diet alone is never the way to successful weight loss.
Exercise helps to burn calories. It builds your body, making it stronger, faster and more efficient. Therefore, both exercise and diet together are the complete key to weight loss success.
It’s still true that the more we move our bodies the more calories we will burn, and the more weight we will shed, despite what the media wants you to think. Some of us Westerners move our bodies less than 5 miles per day. Some of us move a lot more than that. Those of us that move more will subsequently be more fit.
At the same time, losing weight should not be the only goal for someone seeking a healthier lifestyle. Because losing weight is a finite process. Once you reach the weight you want to be, you stop dieting, you stop exercising and could end up right back where you started. Getting fit, losing weight and becoming healthier is comprised of both eating less and moving more, sustaining a healthy lifestyle over a lifetime.
Here’s another example: For all intensive purposes 3,500 calories = 1 lb. of fat.
If someone wants to lose 2 lbs of fat per week they need to create a deficit of 7,000 Calories per week or, 1,000 Calories per day. Sounds like a lot of work, right?They could:
A.) Eat 1,000 calories less per day.
The average Westerner has a BMR of about a 1,200- 1,600 Calories per day.
For many people that would mean eating about 800-1,200 calories per day (the lowest allowed amount). That’s not much food! On top of the difficulty induced, your body will think it is going into a famine and start reducing its metabolic rate and hang on to every ounce of fat – “survival” mode. You will feel tired, sluggish and weary.
B.) Exercise and burn 1,000 calories per day.
That’s about 2 hours of swimming, biking or jogging for a 150 lb. person per day. Every day. No exceptions.
C.) Meet half way – Exercise 500 calories per day and eat 500 calories less per day.
Which one sounds better to you? C right? Because it’s a balance, it’s not one or the other, it’s one and the other.
Exercise offers increased muscle and bone mass, increased strength, improved insulin sensitivity, improved immune function, stronger and more resilient heart muscle, improved lung function, better sleep, less depression, better brain function, better balance, better agility, quicker reactions, and better blood flow to the skin which enhances our gorgeous looks.
When we exercise, we build muscle and when we diet alone we lose muscle, and that’s not good.
While some humans may have genes that make it harder to lose weight even with exercise and diet, for most of us the story is the same: if we eat more calories than we are burning – even if we exercise- we will gain weight. If we eat fewer calories and move more, we will lose weight. It will take longer for some than it will for others, but the benefits are well worth the persistence. If we’re gaining muscle, we have to take that into consideration when we look at the scale.
Losing weight is not a one or the other activity, it’s a lifestyle change including both diet and exercise. Regardless of where you come from, who you are, or what type of society you live in, the healthy lifestyle and weight loss equation are the same!
1. Plos One Hunter Gatherer Hunter-Gatherer Energetics and Human Obesity – http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0040503
2. Hunter Gatherer Clue to Obesity- http://www.bbc.co.uk/news/science-environment-18985141
3. Dieting Vs Exercise for Weight Loss -http://well.blogs.nytimes.com/2012/08/01/dieting-vs-exercise-for-weight-loss
4. Science Daily (July 25, 2012)- http://www.sciencedaily.com/releases/2012/07/120725200304.htm
5. The Walking Site – http://www.thewalkingsite.com/10000steps.html
6. About.com – http://walking.about.com/od/pedometer1/a/steps-per-mile.html