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Monday, July 17, 2006

The Hacker's Diet: Beta Blockers and Persistent Weight Gain

I wrote The Hacker's Diet in the latter half of 1990, about two years after I completed the 1988 diet in which I developed and used the techniques described in the book. After two years of stable weight following the end of the diet, I was reasonably confident that the mechanism I'd discovered for long-term weight maintenance was not only workable (which follows from the laws of control theory and thermodynamics) but something I could live with on an ongoing basis and not backslide from because it was too onerous. Indeed, by 1991 I had already pretty much arrived at the state described near the end of the “Perfect Weight Forever” chapter where I no longer felt the need to plan meals and count calories because having done so had taught me the portion sizes of various foods that balanced the calorie budget. (And since I continued to monitor my weight and compute the trend, any error in estimation would show up in the charts long before it became difficult to correct.)

In most of the fifteen years since I finished the book, that's been the situation; I continue to monitor daily weight and compute the trend (now using the Palm handheld software I developed in 2002), but don't bother to plan meals and count calories because experience has taught me how much to eat. For the last year, however, I've observed a consistent upward tendency in my weight, roughly equivalent to a daily excess of about 200 calories. Now, this has not resulted in my packing on weight, because each time I “bump the band”—observe the trend to rise more than two kilograms above my weight target—I apply the brakes and bring it back down by deliberately cutting about 500 calories a day from my intake, which is unpleasant, but hardly onerous. It would certainly be better, to be sure, to avoid this process and return to the effortless balance I'd maintained in the preceding years, and even more, as an engineer, to understand the cause, especially as I have made no substantial change in what I eat, portion sizes, frequency of meals, nor level of physical activity compared to earlier years. I've turned over this puzzle quite a bit in my mind over the last few months.

Then, today, I figured it out. Ever since that speech I didn't give on Friday the Thirteenth of May 2005, I have been taking a daily dose of a beta blocker (to be precise, 142.5 mg/day of the β1 antagonist metoprolol succinate) as part of a regime to manage the life-long high blood pressure I inherited. Beta blockers also act to stabilise cardiac arrythmias, something in which I've taken an intense interest since that day in May. But, as with most pharmaceuticals, that isn't all they do. The most obvious effect of beta blocker treatment is a reduction in the resting pulse rate. In my case, this ran around 72 beats per minute before, but now averages around 60 and often falls into the mid-50s. Further, the heart rate doesn't “come off the peg” as quickly when you exercise or perform strenuous work: endurance doesn't seem to be affected, but the ability to quickly transition from sitting down to briskly hiking up a steep hill certainly does.

This is just part of a general reduction in the basal metabolic rate—the rate at which the body consumes energy (and thus burns calories) which amounts to about 10% for a typical person. Before starting on the beta blocker, my daily burn rate was about 2200 calories, and if you take 10% of that, you come up with 220 fewer calories a day burned when the metabolic rate was reduced (actually, somewhat less, since calories burned during exercise and other non-resting activities are not reduced as much). Well, there's the 200 calorie discrepancy—amazing, isn't it, how utterly obvious something like this always seems once you've twigged to what's actually going on!

While this was news to me, the connection between beta blockers and weight gain has been observed in clinical trials as far back as the 1980s. This 2004 paper (registration required) provides an overview and cites other, more subtle effects which may also lead to weight gain, including suppression of the breakdown of fat. A 1995 paper, of which only the abstract appears to be available on-line, argues that exercise may mitigate these effects, so those looking for yet another reason to lengthen their lives by getting off the couch have one more if they're taking these pills.

The bottom line is that beta blocker treatment will probably cut your daily calorie burn a tad less than 10%—the more active you are, the less the percent reduction, and, absent a change in activity, you're probably going to have to cut your daily calorie intake by the same fraction to avoid an upward creep in weight. The good news is that those who follow the weight monitoring and management program from The Hacker's Diet won't be blindsided when this happens. They may, as I was, be puzzled for some time as to the cause, but the automatic adjustment of calorie intake will keep them within the tolerance band around their desired weight. Reducing calorie intake shouldn't result in hunger, since you're only matching your intake to burn, which was the status quo ante; the smaller portion size may not look as satisfying on the plate, but it meets your now-reduced calorie requirement just as well.

And, just to stave off questions from concerned readers, I couldn't feel better. The beta blockers and other medicinal molecules have stomped my previously skull-shattering blood pressure right back into the middle of the green zone, and I'm perfectly willing to eat a little less every day to maintain this result. Also, as the author of The Hacker's Diet, it's reassuring to know that the weight management scheme I designed more than fifteen years ago worked when put to the test of an unidentified input it took me more than a year to understand; this means that even when something is going on that you haven't figured out (like the “Chef Bubba” example in the “Losing Weight” chapter of the book), you still won't lose control of your weight until you do manage to identify the cause. Despite being based upon my own experience, this is not a narrow issue: according to a recent newspaper report, fully one in six people in the United States takes beta blockers, which are the fifth most frequently prescribed drug there. Given the prevalence of obesity in the United States, this connection is something to keep in mind.

Posted at July 17, 2006 23:23