Posts Tagged ‘weight loss’

Can you trust the calorie counts on exercise machines?

August 23rd, 2011

After an interesting e-mail conversation with Dr. Yoni Freedhoff of the pull-no-punches Weighty Matters blog, I ended up writing a guest post about some of the factors you need to think about if you ever look at the calorie number that your treadmill (or elliptical or exercise bike or whatever) spits out. Without giving away too much, I’ll say this: if you’re not considering the difference between gross and net calorie burn, you’re kidding yourself! READ THE FULL POST HERE.

Carbs and insulin vs. reward theory as the cause of obesity

August 16th, 2011

For those interested in the cause of obesity, a lengthy post by blogger and neurobiologist Stephan Guyenet is rocketing around the Internet. After a rather testy exchange with Gary Taubes at the Ancestral Health Symposium (which culminated with Taubes offering Guyenet this no-so-friendly advice: “I would just recommend in the future you should pay attention to populations that might refute your hypothesis rather than just presenting populations that support.  That’s always key in science.“), Guyenet decided to write a detailed dissection of Taubes’s carbohydrate theory of obesity, explaining why it’s “not only incorrect on a number of levels, but may even be backward.”

Here’s Taubes’s own statement of the theory in question, as quoted by Guyenet from Good Calories, Bad Calories:

This alternative hypothesis of obesity constitutes three distinct propositions.  First, as I’ve said, is the basic proposition that obesity is caused by a regulatory defect in fat metabolism, and so a defect in the distribution of energy rather than an imbalance of energy intake and expenditure.  The second is that insulin plays a primary role in this fattening process, and the compensatory behaviors of hunger and lethargy.  The third is that carbohydrates, and particularly refined carbohydrates– and perhaps the fructose content as well, and thus perhaps the amount of sugars consumed– are the prime suspects in the chronic elevation of insulin; hence, they are the ultimate cause of common obesity.

Guyenet’s post is an interesting read, and it certainly raises some questions about Taubes’s reductionist approach to obesity (which I’ve criticized in previous posts). It should be noted that Guyenet himself has a Grand Theory of Obesity, which he dubs the “food reward” theory. It basically argues that modern foods trigger reward behaviour in our brains without the accompanying satiety signals that traditional foods would offer. To his credit, he’s more circumspect about trumpeting the powers of his theory: the post I linked to is titled “Food Reward: a Dominant Factor in Obesity.” No doubt that Taubes would have said “the Dominant Factor…” 🙂

Still, my overriding sense is that scientists (and journalists, for that matter) with Grand Theories rapidly become unable to critically evaluate data that conflicts with their theory. Personally, I think it’s highly unlikely that we’ll find a single dominant factor that explains the dramatic rise in obesity over the last few decades, and the endless search for that one magic bullet distracts us from the obvious contributing factors that we already know about.

Being overweight may not extend life after all

August 13th, 2011

Is it good to be a little bit overweight as you get older? That’s the message from a series of large, reputable studies (including one that made lots of news two years ago). The theory is that having a few extra pounds is good as you get old and frail, so that you don’t waste away to nothing if you get sick or break a hip. And the data seems to back up this theory.

But wait a sec. A new study in the Journal of the American Geriatrics Society from researchers at Loma Linda University in California (abstract here, press release here) shows the opposite:

[M]en over 75 with a body mass index (BMI) greater than 22.3 had a 3.7-year shorter life expectancy, and women over 75 with a BMI greater than 27.4 had a 2.1-year shorter life expectancy.

Why the contradiction? Actually, there are some very good reasons. The authors start by explaining some of the potential flaws with the earlier studies that seemed to show that being a bit chubby helped you live longer. The key problem is that the earlier studies measured weight just once, at the beginning of the study, and then waited to see how quickly the subjects died. But people who were skinny at the beginning of the study might have been skinny because they were already sick, possibly without having being diagnosed yet. If you’re skinny because you’re partway through a dramatic weight loss than ends with your death, that’s not quite the same as being thin with a long-term stable weight and healthy lifestyle.

The new Loma Linda study is able to address this problem, along with a few others. It relies on two large studies of Seventh-Day Adventists in California, one in 1960 and the second in 1976. Weight was measured on both occasions, and mortality was monitored until 1988. By looking only at the people whose weight stayed the same (within 5 kg) between 1960 and 1976, you get to study the effects of having extra weight, rather than the effects of gaining or losing it for whatever reason (both of which could have significant effects, but are separate questions).

Another quirk of the study is that Seventh-Day Adventists are forbidden to smoke. So to further eliminate confounders (e.g. people who were thin because they were puffing on cancer sticks), the analysis was able to completely exclude any past or present smokers, plus anyone with any history of coronary heart disease, stroke or cancer at baseline, and still have a total of 6,030 people aged 25-82. The point here is that we’re looking just at the effects of extra weight, stripped away of as many confounders as possible.

And sure enough, higher BMI corresponded to higher risk of death for 75- to 99-year-olds: above 22.3 was bad news for men, and above 27.4 was bad news for women. Obviously this study can’t tell us why there’s a difference between men and women, but the researchers suggest that women may benefit from having a bit more fat because that’s where estrogen is produced after menopause; too little estrogen may leave them susceptible to everything from hip fracture to insulin sensitivity problems. Here’s how the “hazards ratio” (basically your odds of dying relative to the healthiest group) looks as a function of BMI:

So what does this mean? Well, we’re not going to rewrite the medical textbooks based on a few Seventh-Day Adventists in California. It’s just one study, etc. etc. But given the methodological differences between this study and the previous ones, it certainly seems reasonable to wonder whether the apparent paradox of overweight people living longer is simply an artifact of the confounders this study managed to eliminate. I’m not saying you should panic if you’re overweight — I’m just saying you shouldn’t panic if you’re not.

When one twin runs more than the other

June 15th, 2011

Interesting new study from Paul Williams’ National Runners’ Health Study — no, wait, this is a new one, not the one I wrote about a few days ago! This one looks at identical twins to find out the extent to which your body shape is dictated by your genes. Yes, the old nature vs. nurture debate…

Williams has an enormous data set of over 100,000 runners, including 926 identical twins. He explored the relationship between two quantities: the difference in how much a pair of twins ran, and the difference between how much they weighed. Various studies have found that genetic factors account for 40% to 70% of the variation in BMI. But Williams found that the more the active twin exercised, the less genetics seemed to matter. Here’s a graph:

The numbers on the right-hand side represent how much more the active twin runs than the less-active twin. Of course, for some people the results will seem absurdly obvious: the greater the difference in activity levels between two people, the greater the difference in their BMI. Still, it’s a good reminder that genetics isn’t destiny. Here’s what Williams concludes:

Extrapolating the coefficients of Table 3 shows that BMI inheritance might be eliminated completely by running 7.05 km/day (23 mi/wk) in women and 13.51 km/d (60 mi/wk) in men, a projection that is consistent with our previous finding of uncorrelated BMI values in 35 pairs of MZ twins whose running differed by an average of 8 km/d [31], but a projection that should nevertheless be considered with caution.


Burfoot, Noakes, and the ultimate workout

June 14th, 2011

Fascinating post on Amby Burfoot’s Peak Performance blog about a recent Yale study on the mind and appetite hormones. Researchers gave subjects either a high-calorie or a low-calorie milkshake (and told them which one they were getting), then measured the change in ghrelin, a key appetite hormone:

As you would expect, the subjects’ ghrelin levels dropped after the indulgent, high-calorie shake. After all, this thing contained more than 600 calories. It would fill up anyone. When the subjects drank the low-cal shake, their ghrelin levels stayed basically the same.

Here comes the twist: The shakes were identical; they were all moderate-calorie.

So what does this mean? Amby goes on to discuss other phenomena like “sham arthroscopy” and the”world’s best running workout.” The whole post is worth a read, but I found his suggestion for a workout particularly interesting: 5 x 1 mile as hard as possible… then when you’re done, your coach makes you do one more at the same pace:

From this workout, you’ll learn forever that you’re capable of much more than you think. It’s the most powerful lesson you can possibly learn in running.

I agree. And it also made me think of something Tim Noakes told me when I interviewed him last summer. I’d asked about the origins of his “central governor” model, and how coaches might actually apply its lessons in practice. Here’s what he said:

I think all the great coaches always work on the brain anyway. And they get you to run faster because they teach you that you can… I remember the compelling moment in my own rowing career was we used to do 6 times 500 metre repetitions. And one afternoon, we did our sixth and turned around rowing back to the boathouse, and the coach says, ‘No, go to the start again. You’re doing another one.’ So we did another 500. And he said go back. And we did another four. And you know, no one would have believed that we could do that, if you’d asked us… That taught us that you have to teach athletes, somewhere in their careers, that they can do more than they think they can.

As Amby points out, the problem is that you can’t prescribe a workout like that to yourself: you need a trusted authority telling you what to do. This is a really interesting and important point. We keep on discovering that the brain is more powerful than we’d suspected in regulating performance (and even appetite hormones) — but it’s still not clear how we can actually harness these powers.


The more you exercise, the less diet matters

June 13th, 2011

This week’s Jockology column in the Globe and Mail takes a closer look at some new results (which I blogged about back in April) from the long-running National Runners’ Health Study:

At a public debate in May on the relative importance of exercise and diet in battling obesity, Yoni Freedhoff began his opening arguments with some basic physics.

“There’s no debate about whether the laws of thermodynamics exist,” said Dr. Freedhoff, the medical director of the Bariatric Medical Institute in Ottawa. Energy can’t be created or destroyed, so weight loss ultimately depends on burning more calories than you consume. But which side of that equation should you focus on? [READ THE FULL ARTICLE]

The basic finding of the new study is that the more you exercise, the weaker the link between diet and weight. I exchanged a few e-mails with Yoni Freedhoff (of Weighty Matters fame) about this idea, and his initial reaction was that the findings could be interpreted as simply the result of calories burned while running. After all, running 8 km per day (as the “top” group in the analysis does) burns quite a few calories. I tend to think that there’s more going on here (as I explain in the article), but I’d certainly be interested in hearing what others think. Am I making too big a deal about something that’s completely obvious?

Is strength training really better than cardio for weight loss?

May 24th, 2011

I did a radio interview today with Angela Kokott on QR77 in Calgary, and one of the questions we discussed was the perennial claim that lifting weights is better than aerobic exercise for burning calories. It’s a claim that isn’t totally crazy — even the most recent American College of Sports Medicine position stand on weight loss reverses earlier stands by acknowledging the possibility that resistance training could contribute to weight loss by elevating resting metabolic rate, increasing fat oxidation, and making people more active generally. Here’s the funky flowchart they use to illustrate this process:

Still, the “evidence statement” endorsed by the position stand is: “Resistance training will not promote clinically significant weight loss.” In other words, it’s a nice theory, but the studies of actual people losing weight don’t back it up.

The reason I bring this up is that James Fell has a good article in the Los Angeles Times that tackles this topic — in particular, taking on the oft-repeated whopper that every pound of muscle burns an extra 50 calories a day. He turns to Claude Bouchard of Pennington Biomedical Research Center, who offers the following breakdown of resting metabolic rate (RMR):

Brain function makes up close to 20% of RMR. Next is the heart, which is beating all the time and accounts for another 15-20%. The liver, which also functions at rest, contributes another 15-20%. Then you have the kidneys and lungs and other tissues, so what remains is muscle, contributing only 20-25% of total resting metabolism.

The punchline, according to Bouchard: a pound of muscle burns about six calories a day while a pound of fat burns two calories a day. Don’t get me wrong: strength training is great for many reasons, and I certainly encourage everyone (including, reluctantly, myself) to do some. But it’s not a miracle weight-loss technique.


The more you run, the less your diet affects your weight

April 19th, 2011

Another month, another neat paper from Paul Williams’ prolific National Runners’ Health Study, online at Medicine & Science in Sports & Exercise. With his sample of >100,000 runners, Williams took two well-established correlations — those who eat more meat tend to weigh more, as do those who eat less fruit — and checked to see whether these links between diet and weight were affected by how much exercise the subjects did.

The first thing to emphasize: don’t get hung up on whether or why meat and fruits are “good” or “bad.” That’s not what this study is about. It’s just a cross-sectional study, so individual dietary markers (like meat and fruit consumption) may simply be markers of other behaviours. But whatever the reason for these correlations, they’re well established. The question is: if you do lots of exercise, are you less likely to get fat from whatever dietary patterns are associated with high meat and low fruit intake?

The answer is yes:

Specifically, compared to running < 2 km/d, running >8 km/d reduced the apparent BMI increase per serving of meat by 43% in men and 55% in women, and reduced the apparent BMI reduction per serving of fruit by 86% in men and 94% in women.

Williams suggests two possible explanations for this effect:

  • Aerobic exercise trains your body to burn a higher percentage of fat rather than carbohydrate for fuel. In contrast, people who burn a lower percentage of fat compared to carbohydrate are thought to be at higher risk of gaining weight.
  • Exercise improves “coupling between energy intake and expenditure.” In effect, researchers have found that people who exercise more tend to develop stronger appetite cues that tell them when they’re hungry or full. There have been some neat studies of this, where subjects were fed “disguised” drinks that had either high or low energy content. As a later meal, regular exercisers unconsciously adjusted by eating more or less (depending on which drink they’d received) compared to sedentary people.

So why is this important? It goes back to the never-ending “diet versus exercise” debate for weight loss, a false dichotomy if there ever was one. Williams notes that a recent review of epidemiological studies looking for links between reported levels of physical activity and prospective weight gain concluded that they “generally failed” to show any links. This contrasts sharply with Williams’ own findings, which clearly show that “running attenuates age-related weight gain prospectively in proportion to the exercise dose, and that increasing and decreasing exercise produces reciprocal changes in body weight.” He speculates that the difference arises because running is relatively vigorous. It’s also easy to quantify compared to vague epidemiological studies that have subjects estimate how much time they spend playing soccer or mowing the lawn, at what subjective level of effort.

Whatever the mechanism, it’s a good reminder that exercise can play a role in weight control. It certainly doesn’t give you a free pass on your diet — but if you do enough, it seems to give you a little more wiggle room.

Skipping breakfast leads to lead poisoining?

April 7th, 2011

A few months ago, I blogged about the controversy surrounding whether eating breakfast is a good strategy for people trying to lose weight. I (along with expert clinicians like Yoni Freedhoff) am in the pro-breakfast camp, but a few readers offered well-supported arguments against breakfast.

So I’ve been biding my time since then, waiting for a slam-dunk argument — and now I’ve got it! A new study in the journal Environmental Health looked at blood levels of lead in a group of 1,344 children in China. Apparently, it has been shown previously that fasting increases the rate of lead absorption in the gastrointestinal tract. So if you don’t eat breakfast, this daily mini-fast could cause your body to absorb more lead into the bloodstream. Sure enough, after controlling for factors like age and gender, the study found that regular breakfast-eaters (as reported by their parents) had 15% less lead in their blood than regular breakfast skippers.

In all seriousness, this is unlikely to be relevant to anyone who doesn’t have lead paint on their walls or a toy-box full of lead toys. I just thought it was interesting — and it does show that eating patterns and timing do affect how your body processes the food (and heavy metals) that pass through your gut. Overall, the research on breakfast and weight control is still pretty muddled and conflicting. I remain pro-breakfast, but I realize this study isn’t going to win anyone over!

UPDATE April 8: Perfect timing: I just noticed that Peter Janiszewski over at Obesity Panacea has a post on a new prospective study showing that breakfast-skippers aren’t just heavier in a cross-sectional analysis, but also tended to gain the most weight after a two-year follow-up. Still suffers from the same flaws as any non-randomized trial (i.e. the skippers could be the ones who are already battling weight problems), but an interesting finding nonetheless.

Wait, maybe thermostat settings really do affect weight

March 11th, 2011

I can’t resist posting this follow-up to last month’s discussion of a paper proposing that one of the reasons we’re getting fatter is that we heat our houses too much. Where’s the evidence, you demanded? Ask and you shall receive…

Peter Janiszewski over at Obesity Panacea recently had an interesting post describing a prospective study that followed 1,597 people for six years, looking for “relatively unexplored” factors that might predict who becomes obese and who doesn’t. One of the factors they looked at was the temperature people kept their homes at:

[A] twofold increased risk for both incident obesity and hyperglycemia was estimated in subjects living at an indoor temperature >20 C.

While there are all sorts of cause-and-effect questions to worry about, I should point out that the 315 people who were obese at the start of study weren’t included in the analysis of what caused obesity; similarly, the 618 people who started with hyperglycemia were excluded from the analysis of what caused hyperglycemia. So it wasn’t just that people who are already obese prefer warmer temperatures (which would be the opposite of what I’d naively expect anyway).

Of course, I should include the disclaimer from the paper:

It might be hypothesized that metabolic processes are favorably affected by an ambient temperature within the thermal neutral zone, that is, not requiring energy expenditure to be allocated to maintaining a constant body temperature. However, no evidence exists to support this and socioeconomic factors might confound these associations.

As Peter noted (rather forcefully!) in his blog post, this idea is way out there on the fringe. And no one, including me, is suggesting that it’s a dominant factor in causing obesity. But perhaps it’s actually worth considering as one of the elements in an “obesogenic environment.”