Posts Tagged ‘weight loss’

Less sleep makes food more rewarding

February 3rd, 2012

There’s plenty of evidence that lack of sleep puts you at higher risk of gaining weight. A new Swedish study in the Journal of Clinicla Endocrinology and Metabolism (press release here, abstract here) offers some new insights with fMRI brain scans:

We already know that obese people tend to find food more rewarding, as indicated by brain scans of activity in the anterior cingulate cortex:

Higher activation of this brain region has been found in obese compared with normal-weight subjects when anticipating food, suggesting that the rewarding quality of food is enhanced in obesity.

The study took a dozen volunteers and kept them up all night, then looked at their brain’s response to images of food. Compared to after a normal night of sleep, they observed the same changes that you see in obesity: stronger activation of the ACC, indicating higher dopamine signalling. You want more food than normal, because food makes you feel better than it normally would. As the graph on the right shows, those with the biggest changes in brain activity also reported the biggest appetite.

A study like this, where the subjects stayed up all night, isn’t a great way of figuring out what happens in the much more common situation of, say, getting half an hour less sleep than you need, night after night for weeks or months on end. But other studies looking at appetite hormones like ghrelin and leptin suggest that the effects are similar: too little sleep = greater appetite relative to energy needs.

Of course, this leaves us with a riddle: if you have to get up an hour early to fit your workout in, do the benefits outweigh the downsides? That depends on a  lot of things, but my general sense is that exercise has so many benefits that it’s still worthwhile. The real answer, of course, is to organize your life so that you can sleep enough and get some exercise.

Two ways to trigger brown fat

January 30th, 2012

Gina Kolata had a New York Times article last week about “brown fat” — the strange, recently discovered (in adult humans, at least) type of fat that burns lots of calories:

A new study finds that one form of it, which is turned on when people get cold, sucks fat out of the rest of the body to fuel itself. Another new study finds that a second form of brown fat can be created from ordinary white fat by exercise.

So what does this mean? No one is really sure at this point, since it’s only been a couple of years since we even realized that it existed in adult humans. Do people become obese because they lack brown fat? Or do they lose brown fat when they become obese? Or does it just seem as if obese people have less brown fat because they don’t get as cold as leaner people, so their brown fat remains dormant? We don’t know.

Still, the article made me think of a pair of posts I wrote last year (here and here) about research that linked the rise in obesity rates with a parallel rise in the typical thermostat settings in U.S. and U.K. homes. Could the warmer ambient temperatures that we expect these days have anything to do with higher rates of obesity? There are many reasons to be highly skeptical about this idea… but the fact that brown fat turns on and starts plowing through calories at colder temperatures does provide a plausible mechanism — beyond shivering — for how temperature could play a role.

Of course, researchers say, they are not blind to the implications of their work. If they could turn on brown fat in people without putting them in cold rooms or making them exercise night and day, they might have a terrific weight loss treatment. And companies are getting to work.

We don’t really need to wait for “companies to get to work,” though. We already know how to trigger brown fat without any pills: even if you don’t go for turning down the thermostat (and I don’t believe there’s anywhere near enough evidence to advise that), the other option — exercise — sounds like a pretty good idea.

The “Fat Trap” and biological determinism

January 3rd, 2012

I’ve received a few e-mails asking what I thought of Tara Parker-Pope’s recent New York Times Magazine piece (“The Fat Trap”), which talks about how the body fights off your attempts to make it lose weight. In general, I thought it was a good piece. The basic message I came away with is the same one I hear from people like Yoni Freedhoff: if you want to lose weight — and keep it off — you have to do so using an approach that you’re prepared to maintain for the rest of your life. You can’t go on a diet for six months, lose weight, and then resume your previous diet and lifestyle (or even go halfway back to your previous diet and lifestyle!). Many (perhaps even most) people who are trying to lose weight still see it as a temporary transitional stage. That’s not how the body works, and the more widely that message is spread, the better.

Having said that, a quick note about the apparent “biological determinism” that opposes weight loss. Parker-Pope discusses some of the research by Rupert Leibel’s group at Columbia University, in which subjects are placed on carefully controlled liquid diets to make them gain or lose weight in order to observe what changes take place in their metabolism:

The research shows that the changes that occur after weight loss translate to a huge caloric disadvantage of about 250 to 400 calories… Muscle biopsies taken before, during and after weight loss show that once a person drops weight, their muscle fibers undergo a transformation, making them more like highly efficient “slow twitch” muscle fibers. A result is that after losing weight, your muscles burn 20 to 25 percent fewer calories during everyday activity and moderate aerobic exercise than those of a person who is naturally at the same weight.

I also discuss this research in (plug alert!) my book, Cardio or Weights. And the part Parker-Pope doesn’t mention is that, when you feed people extra calories, exactly the opposite adaptation takes place. In other words, after gaining weight, your muscles burn about 15 percent MORE calories during everyday activity and moderate aerobic exercise. Parker-Pope presents the research as a part of the explanation for why it’s near-impossible to lose weight — but looking at the whole picture, that would mean that it should be impossible to gain weight in the first place! Sure, the barrier is a little bigger when you’re trying to lose weight (20-25% vs. 15%). But the point is, these changes in metabolic efficiency aren’t insurmountable barriers — otherwise no one would ever change weight at all.

Fitness vs. fatness, again

December 9th, 2011

Another study weighs in on the question of whether fitness or fatness is a more important marker of health (abstract here, press release here). This is a nice, clear one. The researchers followed 14,345 men (with an average age of 44 at the start of the study). They did two detailed physical exams just over six years apart (on average), then followed the men for another 11 years to see which ones died, and why.

Basically, there are two variables of interest:

  1. Did the men lose weight, gain weight, or stay stable between the two exams?
  2. Did the men lose fitness (as measured by a maximal treadmill test), gain fitness, or stay stable?

The result: those who maintained or improved fitness were less likely to die by ~30-40% compared to those who lost fitness — even when you control for factors like BMI. Obvious and expected.

But what about weight? As you’d guess, those who gained weight were more likely (by 35-39%) to die of heart disease than those who lost weight or stayed stable. BUT if you take into account changes in fitness, then the effect of changes in weight almost disappeared. So this is further support for Stephen Blair’s argument that it’s fitness that matters, not fatness, when it comes to predicting health (and Blair is, indeed, one of the authors of this paper). As the press release puts it:

“This is good news for people who are physically active but can’t seem to lose weight,” said Duck-chul Lee, Ph.D. […] “You can worry less about your weight as long as you continue to maintain or increase your fitness levels.”

But let me add one clarification. Whenever this topic comes up, I often hear from people who say something along the lines of “See, BMI is meaningless! This proves that doctors should never even measure weight, because it doesn’t predict health.” Not quite. Let me reiterate: those who gained weight in this study were 39% more likely to die of a heart attack than those who lost weight. The reason weight gain doesn’t stay as an independent predictor of death is that those who gained weight also (on average) lost fitness, and those who lost weight also (on average) gained or maintained fitness.

So the very important message that this study reinforces is that it’s fitness that matters most. Keep exercising even if you don’t see changes in your weight, and you’ll be gaining extremely important benefits. But don’t interpret it to mean “it doesn’t matter if I gain weight, because weight is meaningless as a health marker” — because there’s a decent chance (though it’s certainly not guaranteed) that if you’re gaining weight, you’re also losing fitness.

(One final caveat: as the press release notes, 90 percent of the men were either “normal weight” or “overweight” — i.e. BMI under 30. So you can’t assume that the same lack of problems would hold true for the “obese” category with BMI over 30.)

Which childhood activities predict healthy adulthood?

December 8th, 2011

Encouraging kids to be more active is one of those motherhood-and-apple-pie goals that pretty much everyone sees as an excellent idea. Still, it’s worth asking: do the kids who are most active grow up to be the adults who are most active? And perhaps more importantly, which types of childhood activity (school phys ed? sports? unstructured play? walking or biking to school?) are most effective at establishing lifelong habits of physical activity?

Researchers in Australia just published a big study on the British Journal of Sports Medicine that followed up on 2,201 kids who had completed a detailed physical activity questionnaire way back in 1985, when they were between the ages of 9 and 15. The goal was to figure out whether and how “frequency and duration of discretionary sport and exercise (leisure activity), transport activity, school sport and physical education (PE) in the past week and number of sports played in the past year” when they were kids influenced their activity patterns as adults between the ages of 26 and 36.

Depending on how you look at it, the results are either very simple or very complicated. You can delve into all the nitty-gritty details of which childhood factors seem linked to which adulthood factors — and find puzzling and seemingly contradictory trends like this:

Higher levels of school sport among older males were associated with a 40% increase in the likelihood of being in the top third of total weekly activity in adulthood, but with a 40% lower likelihood among younger males.

Does this mean that school sport is bad for 9- to 12-year-olds and good for 13- to 15-year-olds? Probably not. As discussed earlier this week, when you search for links between large numbers of variables in a big collection of data, you’ll always find some relationships that appear statistically significant but in fact have little or no meaning. When you look at this data as a whole, there are a few “significant” associations, but there’s no overall trend, as the researchers acknowledge:

[F]ew associations were evident, most were relatively weak in magnitude and, for some activities, inconsistent in direction.

In other words, if you take a group of 12-year-olds and look at how active they are, you’ll have very little ability to predict which of those kids will have healthy, active lifestyles 20 years later. This is a bit of a bummer, because it makes it harder to decide exactly what types of physical activity are most useful for forming lifelong activity patterns. But don’t make the mistake of thinking that this implies that school phys ed (and other childhood physical activity) isn’t useful! Phys ed for 12-year-olds may not produce healthy 30-year-olds, but it sure as heck produces healthy 12-year-olds — and that’s a worthwhile goal on its own.

And hey, there’s also the fact that (as Gretchen Reynolds wrote about in the New York Times last week), a little bit of physical activity makes you perform better on tests. What kid wouldn’t want a boost of brain-derived neurotrophic factor coursing through his veins and boosting his memory as he heads back to math class?


The activitystat hypothesis: do we have an exercise set point?

October 27th, 2011

If you do a vigorous workout in the morning, will you be correspondingly less active for the rest of the day, so that your total physical activity ends up being the same as if you hadn’t worked out at all? That’s the basic gist of the “activitystat” hypothesis, which Gretchen Reynolds described in a New York Times article last week (thanks to Ed for the heads-up!). It’s also the topic of a pro vs. con [EDIT: had the links backward before -AH] debate in the current issue of the International Journal of Obesity (full text free available).

Reynolds describes several interesting studies that line up in favour of or against the theory, including one (from the same issue of IJO) that compared three British elementary schools with very different amounts of in-school physical activity. Here’s what that study found:

You can see that, for both “total physical activity” and “moderate and vigorous physical activity,” one group had much higher levels in school than the other two, but compensated by doing less outside school. On the surface, it seems like a pretty compelling argument in favour of the activitystat hypothesis.

My take: somewhere in the middle, as usual. It would be ludicrous to claim that the body doesn’t regulate physical activity based on previous exertions to some degree. Do a one-day study of “voluntary movement” among people who have run a marathon that morning, and of course you’re going to find that they chill out more. At the opposite extreme, it would be equally silly to argue that all people everywhere in the world do exactly the same amount of physical activity. Or that any given person’s physical activity stays essentially constant over long periods of time  — again, think of someone who goes from sedentary to marathon training: no amount of fidgeting or taking the stairs will add up to the exertions of 100-mile weeks. (For more examples of the role of environment in determining activity level, read the “con” commentary I linked to above. E.g. Nandi children in Kenya who grow up in the countryside are more active overall than Nandi city kids — an obvious result, but one that clashes with the activitystat idea.)

So the relevant question isn’t “Do compensatory mechanisms exist?” It’s “Do they matter, and are they insurmountable?” As lovely as the data from the British school study is, I don’t find it convincing. The school with the highest in-school physical activity was a fancy boarding school in the countryside, while the other two schools were urban. If the boarding-school kids play an hour of cricket in phys ed every day, the fact that they don’t choose to go play an hour after school doesn’t necessarily mean that the activitystat is limiting them. Maybe they just want to (or have to, depending on the other extracurricular requirements of the school) do something else.

One final point: it would be interesting to stratify those results based on the activity levels of the kids. Does the apparent activitystat mechanism apply equally to the most active and least active kids? Because if there are some kids who, left to their own devices, only get a total of 50 minutes of moderate/vigorous activity per week, then giving them 100 minutes a week in school is going to benefit them — and there’s nothing any activitystat can do to stop it!

Is leisure-time physical activity irrelevant?

October 13th, 2011

Here’s a great example of how two people can look at the same data and reach totally opposite conclusions. Over at Obesity Notes, Arya Sharma just blogged about a new study surveying what types of activities (leisure, occupational, household) burn the most calories for people. The title of the post: “Why Leisure-Time Physical Activity is Irrelevant.” He reaches this conclusion because the study found that leisure-time physical activity accounts for at most 10 percent of total energy expenditure, even for the most active people.

To explain why I find this logic to be a bit strange, let me make an analogy. Let’s say we’re debating why kids these days no longer know how to do long division. A study comes out saying that only 10 percent of elementary schools currently teach long division. Possible conclusions:

  1. So few kids receive long division instruction that teaching is clearly irrelevant to their long-division ability (or lack thereof).
  2. The results are consistent with the theory that the almost total lack of long division instruction may contribute to kids’ observed inability to do long division.

To me, it seems like Dr. Sharma is choosing the first option. Now, there’s plenty in his post that I agree with, particularly the suggestion that we should emphasize things like active transport that use energy in constructive, goal-directed ways. But the blog post has a strong current of antipathy toward the whole concept of exercise that I find surprising. For example:

[W]e have originally evolved the ability to be physically active primarily to hunt, gather, fight, flee and reproduce. The notion that any reasonable person would actually engage in a significant amount of ‘non-utilitarian’ (read: useless) physical activity beyond early childhood… is something that physical education enthusiasts (and governments) would wish for, but nature failed to put into our genes.[…]

Yes, there is a small proportion of the population, who (strangely enough) continues to enjoy leisure-time physical activity well into adulthood. The vast majority, however, prefers to much rather spend their leisure time reading, playing a musical instrument, engaging in arts and crafts, or simply lying on the couch watching professional sports. This is perfectly reasonable and completely normal human behaviour.

I understand that Dr. Sharma is, to an extent, simply counterbalancing the relentless (and misplaced) societal message that tells obese people that they’re abnormal freaks who lack enough self-discipline to take the “simple” steps like exercise that would help them lose weight. But I find it absolutely baffling that he’s arguing, on the one hand, that evolution dictates that we stop physical play after adolescence, but on the other hand suggesting that we’re wired to enjoy mastering a musical instrument (a highly cognitively and sometimes physically demanding task) or watching the very sports that apparently cease to have meaning for us when we become adults. The net result is that, next time I see Dr. Sharma quoted on the question of whether exercise can play a role in preventing weight gain, I won’t be able to avoid the feeling that his answers are coloured by a deep personal dislike of exercise in addition to his reading of the research.

And there’s another point, too. Dr. Sharma talks about “policy changes” and “workplace initiatives” to promote things like active transport, which he views as far superior to  “useless” exercise. But to me, that seems like a false dichotomy. If I have the option of taking the subway to work, but a policy initiative “encourages” me to bike instead, how is that different from voluntary exercise? In both cases, I’m choosing to burn calories that I don’t have to burn, because I believe I will derive a benefit from doing so. Is evolution really wiring me to abhor biking if I head north along the Humber River trail, but to love it if I head east toward downtown along the subway line that could carry me there much more quickly and effortlessly?

And a final thought. Let’s distinguish between what’s “easy” (or what Dr. Sharma would consider “normal”) and what may or may not be causal or contributing factors to obesity. Speaking purely hypothetically here, if a large, well-designed study were to show that two hours of moderately hard daily exercise prevented weight gain in 98% of people, Dr. Sharma might quite rightly say that this finding is irrelevant — after all, how many people will be willing to do that much exercise? But in that case, it would no longer be correct to argue that physical activity can’t prevent weight gain. The current moment in history that we’re living through is precisely the product of our having followed what’s easy/normal at every branch in the road. To move to a different place, we’re going to have to take a path of greater resistance. Whether that means banning cars, restricting processed foods, or exercising more than seems “normal” remains to be seen. But it’s no longer enough to say “I can’t do that, evolution won’t let me” — because that’s what got us here in the first place.

Do you need a bit of extra fat to stay healthy as you age?

September 25th, 2011

This week’s Jockology column in the Globe and Mail tries to untangle conflicting data about whether being moderately overweight increases or decreases your lifespan:

It’s a surprising, subversive and very, very popular idea.

Over the past few years, several studies – including a 2009 analysis of Statistics Canada data – have suggested that being a bit chubby as you get older, far from being a health risk, may actually help you live longer. The extra weight, the thinking goes, could help cushion you from the inevitable slings, arrows and hip fractures of old age.

But the newly published results of a three-decade-long study of clean-living Seventh-Day Adventists in California suggest that you might want to go easy on those early-bird specials after all. When confounding factors such as skinny smokers were removed, the effects of extra weight were clear – and bad – even for those older than 75… [READ THE WHOLE ARTICLE]

The article is accompanied by a graphic by Trish McAlaster, which includes a bit of info on the recent study showing aerobic exercise targets visceral fat more effectively than strength training, which targets subcutaneous fat:

Obesity, delayed gratification and the Marshmallow Test

September 1st, 2011

A new follow-up to the famous Marshmallow Test study on delayed gratification has just been published. Back in the 1960s, researchers tested a group of pre-school children on how long they could resist the temptation of an immediate reward (e.g. a marshmallow) in favour of a “larger, later” reward (e.g. two marshmallows). They followed these kids for decades, and found that the kids who were able to hold out the longest ended up less vulnerable to outcomes ranging from obesity to divorce to crack cocaine addiction.

The newest update, just published in Proceedings of the National Academy of Sciences (full text freely available here, press release here), with the subjects now in their 40s, confirms that the kids who were “high delayers” are still “high delayers,” and the kids who were “low delayers” are still “low delayers.” For the first time, they used brain scanning to determine that the high delayers showed greater activation in the prefrontal cortex while the low delayers had greater recruitment of the ventral striatum. This may reflect the differing use of of different “cold” and “hot” modes of cognition in choosing between competing impulses.

Anyway, I’m not going to go into great depth about the neuroscience here (as noted above, those who are interested can read the full paper freely). What caught my attention was the following quote in the press release:

“This is the first time we have located the specific brain areas related to delayed gratification. This could have major implications in the treatment of obesity and addictions,” says lead author Dr. B.J. Casey, director of the Sackler Institute for Developmental Psychobiology at Weill Cornell Medical College and the Sackler Professor of Developmental Psychobiology.

One of the interesting debates that I’ve become more attuned to in following the blogs of people like Yoni Freedhoff and Arya Sharma is the tendency to ascribe moral failings — a lack of willpower and unwillingness to make the “right” choices — to obese people. Dr. Sharma frequently argues that “Eat Less, Move More”-type advice is useless for losing weight, because it fails to understand the “countless ways in which the psychoneurobiology, energy physiology and metabolism in anyone who has lost weight” drive you to regain that weight.

So in this picture, does increased power of delayed gratification have any role in treating or avoiding obesity? Or are the biological imperatives too strong for anyone’s self-control? Dr. Sharma had a very interesting post a couple of weeks ago about the role of personal choice in weight loss, responding to a recent paper in the Journal of the American Dietetic Association. He doesn’t reject the role of impulse control in weight loss — in fact, he suggests it should be considered:

Recognising and fully acknowledging how the brain’s neural circuitry that underlies these behaviours interacts with (and is thus ultimately responsive to) environmental situations and cues can perhaps provide a far more realistic and effective counseling strategy.

Of course, losing weight and avoiding weight gain in the first place are two distinct questions — and in the long term, any success we have in tackling society’s growing levels of obesity will probably come from helping future generations avoid obesity in the first place. The Marshmallow Test data does tell us something interesting: that you can predict who’s most likely to become obese based on tests of brain function in pre-school. That has nothing to do with resting metabolic rate, aptitude for sports, or even what they’re being fed at home.

Obviously, this trait isn’t the root of the problem. Presumably humans have always been born with varying degrees of delayed gratification; it’s only in our modern society that low delayers are at risk of obesity. This is consistent with the idea of an “obesogenic environment” — a world with a copious oversupply of calorie-dense food, convenient labour-saving devices always available, ubiquitous advertising to tempt us into taking the first marshmallow.

But still… it suggests that choices matter. I realize this starts to sound like a moral judgement (i.e. obese people must have made the “wrong” choices), but I don’t mean it that way. In fact, the Marshmallow Test tells us these choices are, to some extent, hardwired into us. But by acknowledging the role of choices, and understanding how and why the “wrong” choices are made, perhaps we can increase our odds of making the right choices. Dr. Sharma suggests a few ways this might work in the post I quoted from above. Another option: the idea of “brain training” is in disrepute right now, partly because it was so dramatically overhyped and oversold a few years ago, but maybe it’s something to consider. It’s a topic that comes up (peripherally) in the Jockology column I just wrote for next Monday’s Globe, and I’m looking forward to seeing more research on it.

Cardio vs weights for visceral and liver fat

August 30th, 2011

A new study in the American Journal of Physiology revisits a very familiar topic — cardio versus weights — to determine which is better for reducing dangerous visceral and liver fat. A total of 155 subjects completed one of three eight-month training programs:

  1. Aerobic (AT): ~12 miles per week at 75% VO2max;
  2. Resistance(RT): 3 days a week, 8 exercises, 3 sets of 8-12;
  3. Aerobic/resistance (AT/RT): both the above programs combined.

At the end of the eight months, they used some pretty sophisticated tools to measure the outcomes, including CT scans to measure levels of visceral and liver fat. Here are some of the key outcomes:

And here’s how the researchers sum up the findings:

First, a resistance training program–even a very substantial one–did not significantly reduce body mass, visceral fat, liver fat or ALT liver enzyme levels. RT also did not reduce total abdominal fat, nor did it improve fasting insulin resistance. Second, in contrast to RT, a typical vigorous AT program resulted in significant reductions in visceral fat, liver fat and abdominal subcutaneous fat, and also led to improvements in circulating ALT and HOMA (fasting insulin resistance).

The results aren’t too surprising: as the researchers note, this particular aerobic training program likely burned about 67% more calories than the resistance program. It does seem a bit strange to me that adding resistance training to the aerobic training seems to make things worse rather than better — but the overall analysis in the paper says that AT and AT/RT are statistically indistinguishable. In other words, the weights add nothing. Don’t get me wrong: weights are useful for a lot of things, and this study was only testing a few specific outcomes. But on those outcomes — and they’re very important ones, particularly if you’re overweight — cardio trumps weights.