Thursday, December 29, 2011

Why We Struggle to Maintain Weight Loss

Tara Parker-Pope of The New York Times has written an excellent summary of research on set point theory, that is, the body's tendency to defend a higher weight after weight loss. And some of us may just have to work harder to maintain weight loss because of other genetic factors.

This research can be used as an excuse for weight regain - "What's the use?" or "My genes made me do it" - or as information that can help us forgive ourselves for sometimes falling short of our goals. Of course, I recommend it as a source of compassion, not an excuse for poor eating habits.

Tara Parker-Pope's article

The research also supports the idea that gastric bypass surgery resets the set point that the body will defend going forward. Surgery is not a simple engineering change. Rather, it starts a complex biochemical process that supports weight loss until the new set point is reached.

Thursday, September 29, 2011

Does Preoperative Weight Loss Affect LONG-Term Postoperative Weight Loss?

Some surgical weight loss programs require that, in preparation for bariatric surgery, patients lose a certain amount of weight. This might be a fixed amount, such as 25 pounds, a percentage of total body weight, or a percentage of excess body weight. To my knowledge there are no guidelines from the American Society of Metabolic and Bariatric Surgery (ASMBS) in favor of or opposed to this requirement, as it pertains to weight loss. The ASMBS guidelines do recommend presurgical weight loss in order to reduce liver size and thus decrease surgical risk.

In the previous post, we reviewed a study looking at short-term weight loss after Roux-en-Y gastric bypass surgery. Today we will consider a study conducted at a single medical center that recommends that patients lose 10% of their total body weight before surgery. These clinician researchers state that their experience tells them that preoperative weight loss improves weight loss outcome in the long term, and their data support their expectation. However, as we'll see, there are some problems with the study that limit the validity of that claim.

Let's take a look at the results. Some number of patients were recruited for the study and their preoperative weight loss was documented. We are not told how many people initially participated in the study, only that 150 patients were available for follow-up after 3 years and 95 were available after 4 years.

Right off the bat, there is a question. How many people were unavailable after 3 or 4 years, and, more importantly, why? Were there 200 or 500 or 1,000 participants who signed on to the study in the preoperative phase? We don't know, and this means we also don't know why people were unavailable. Did they simply move away? Did they stop coming in for medical care for some other reason relevant to their weight loss? We also cannot consider how - or if - the dropout rate affects the results. Maybe the 150 patients available after 3 years and the 95 available after 4 years had some special characteristics that set them apart from the general population of gastric bypass candidates. We cannot determine this from the article.

The data clearly showed exactly what the researchers expected: a nearly linear, statistically significant correlation between the weight a patient lost before surgery the weight they had lost at 3 and 4 years out. Percentages of both total body weight and excess body weight followed this relationship.

Another problem with the study: no control group. It is a purely correlational study. This wouldn't be a problem if the researchers hadn't used the word "causation." OUCH! Remember from Intro Psych (and many other intro science courses) the 3 requirements for a true experiment: random sampling from the population, random assignment to groups, and the presence of a control group. Based on what is reported in this article, none of these conditions were met.

So, while intuitively it sounds logical that preoperative weight loss will solidify behavioral changes and ultimately influence long-term weight loss, I'm still looking for evidence that this claim can be supported. What is known is that preoperative weight loss has many other benefits for the patient, such as reduced liver size at the time of surgery (reducing the risk of converting a laparoscopic procedure to an open one), shorter operating time, and fewer surgical complications. These factors alone speak to the importance of starting weight loss as early as possible.
Alger-Mayer, S., Polimeni, J., & Malone, M. (2008). Preoperative Weight Loss as a Predictor of Long-term Success Following Roux-en-Y Gastric Bypass. Obesity Surgery, 18 (7), 772-775 DOI: 10.1007/s11695-008-9482-2

Wednesday, May 18, 2011

Does Preoperative Weight Loss Affect Short-Term Postoperative Weight Loss?

Mental Health Blog Party Badge

May is "Mental Health Month" and today is "Mental Health Month Blog Party," an initiative of the American Psychological Association's Public Education Campaign. Today, bloggers who write about mental health issues will be linked to on APA's public information web site:

So, since every bariatric surgery patient is indoctrinated with the message, "Bariatric surgery is a tool, not a panacea, and I know I have to make lifestyle changes to maintain my weight loss," I thought I would blog today about the value - or lack thereof - of losing weight before having surgery. Some bariatric surgery programs encourage, or even require, prospective patients to lose some amount of weight before having their procedure.

After all, doesn't it make good intuitive sense that solidifying some of those important behavioral changes would lead to a better outcome? Researchers at the Stanford School of Medicine asked that question and reported their results in today's article.
Eisenberg, D., Duffy, A., & Bell, R. (2010). Does Preoperative Weight Change Predict Postoperative Weight Loss after Laparoscopic Roux-en-Y Gastric Bypass in the Short Term? Journal of Obesity, 2010, 1-4 DOI: 10.1155/2010/907097

The authors question two basic assumptions in bariatric surgery research and practice - that preoperative weight loss indicates an individual's intrinsic motivation for behavior modification, and that intrinsic motivation is a valid predictor of outcome. Some institutions may deny patients bariatric surgery when those patients do not demonstrate sufficient commitment by losing weight on their own.

The researchers deserve credit for designing a very well-controlled study: all 354 study participants had laparoscopic Roux-en-Y gastric bypass surgery by the same surgeon at a single institution. All preoperative and postoperative care followed the same guidelines. Large surgical centers tend to have dedicated well-trained staff and large patient volumes. They lend themselves to this type of large prospective study.

Of the 354 patients having surgery, 256 were available for evaluation 1 year later and were included in the study. Of these patients, 125 lost weight before surgery, 104 gained weight, and 27 had no change. A statistical analysis did not find a significant correlation between weight lost (or gained) before surgery and weight lost in the first year.

Thus, the authors conclude (correctly, given their assumptions and research question) that preoperative weight loss should not be required prior to Roux-en-Y because preoperative weight change does not affect 1-year outcomes . . . assuming 1-year outcomes are all one is interested in.

But what about longer-term outcomes? It is pretty much a given that the first year post-op will result in significant weight loss. That's not where the problems set in. Continuing to lose weight and maintaining that weight loss after the first 12-24 months is where the challenges lie. And research tells us that long term success requires long-term behavior changes.

So the next question is . . . Does preoperative behavior change affect behavior change and weight loss in the long term, say 3-5 years? In other words, does the intuitive assumption that the sooner one starts behavior change the longer and stronger those new habits are likely to remain? Stay tuned.

And Happy Mental Health Month!