Genes for Weight and Weight Gain are Different

We know from twin studies that measures of weight (e.g. BMI) tend to be highly heritable - i.e. monozygotic twins are far more likely to resemble each other in terms of weight than dizygotic twins.

We also know that the ability to gain (and lose) weight is very much determined by genetic factors - i.e. for the same degree of excess energy (or energy restriction), monozygotic twins tend to resemble each other in weight gain (or loss) more than dizygotic twins. For e.g. identical twins lose virtually the same amount of weight following obesity surgery, when surgery is performed in the same setting (Hagedorn et. al).

Given this relationship, one may easily assume that genes that control body weight are the same that control weight gain.

A new study by Jacob Hjelmborg from the University of Southern Denmark, Odense together with colleagues from Finland, Italy and the US, just published in OBESITY, suggest that this may not be the case.

Hjelmsberg and colleagues anlaysed data from the longitudinal twin study of the cohort of Finnish twins (N = 10,556 twin individuals) aged 20-46 years at baseline followed up for 15 years.

Simply stated, they found a high level of heritability of BMI levels at baseline (we knew this) and a relatively high heritability of weight gain over the observation period (this is also not new).

However, in their models, it turns out that the two phenomena only show rather modest correlation at the genetic level.

What this means is that while both baseline BMI and weight gain are genetically determined, they are probably each regulated by a different set of genes.

So, while one set of genes may determine how big you are, other genes may determine how large you can get.

We know that some people are large and just stay that way all their life without losing or gaining much. Others may start out at a given size and end up gaining a lot of weight. All depends on your genetic background (and of course how this interacts with your lifestyle and other environmental factors).

Just a reminder how complex genetics actually is.

AMS
Edmonton, Alberta

Why Hunger Makes You Eat Crap

The best recipe for poor food choices and weight gain is to only eat when you are hungry.

This is best done by skipping meals and allowing yourself to get so hungry that you will end up eating anything edible, no matter how bad for you.

Obviously, if you are hungry and have the choice, last night's leftover pizza will prevail over carrot sticks.

So why is it more difficult to make healthy food choices when you are hungry?

Because healthy foods are seldom your favorite foods and usually not the ones that trigger your reward centres and make you feel happy and content.

Hey wait a minute! Did you not in a previous blog entry remember me making the distinction between hunger (homeostatic) eating and appetitive (hedonic) eating?

Well, it turns out the two systems are more closely linked than we may have thought - at least according to a new paper by Saima Malik and colleagues from McGill University, Montreal, Canada, just out in CELL METABOLISM.

Malik and colleagues infused the "hunger-hormone" ghrelin into volunteers and used functional MRI to look at what parts of the brain were activated in response to pictures of junk foods or scenery (controls).

It turns out that not only did ghrelin (as expected) increase the sensation of hunger, but it also increased brain activity in the amygdala, orbitofrontal cortex, anterior insula, and striatum which form part of the mesolimbic reward system involved in addictive behaviours.

This finding is new, because so far ghrelin was largely associated with the homeostatic system - i.e. the system that is more concerned with ensuring energy balance rather than the hedonic system - i.e. the system that is more about the reward you get from eating foods you like.

When you think about it, this finding sure makes sense. After all if you are hungry (and have a choice) you may as well eat the foods that you enjoy.

Unfortunately in today's world that may also mean that you are more likely to chose energy-dense foods that make you feel good, which in turn makes you eat too much - a sure recipe for weight gain.

So while in clinical practice it may make sense to distinguish between homeostatic and hedonic hyperphagia, it is important to remember that biologically the systems are linked and ingestive behaviour may well display characteristics of both systems at a given meal.

It is indeed a fine line between biological need and addiction.

AMS
Edmonton, Alberta

Does Presurgical Weight Loss Predict Outcomes?

Contrary to popular belief, patients who undergo obesity surgery do indeed have to make substantial lifestyle changes to be successful - obesity surgery is therefore never a "quick fix".

Therefore, many bariatric programs, including ours, often use modest presurgical weight loss as a screening tool to determine whether patients can indeed make lifestyle changes that would help them be successful after obesity surgery.

The theory is that if someone is unable to make even modest changes to their lifestyles before surgery, they will have difficulty making those changes after surgery, thereby limiting their chances for success.

But does presurgical weight loss truly predict outcomes?

This question was examined by Bushr Mrad and colleagues who performed a retrospective chart review of 562 patients who underwent surgery in our program. The results of this study were just published in the American Journal of Surgery.

One hundred forty-six patients met the inclusion criteria (23 men and 123 women). The mean age was 39.5 years, and the mean body mass index (BMI) was 52.6 kg/m(2). Comorbid disease includes diabetes (15.7%), hypertension (30.8%), mental illness (38.4%), and musculoskeletal disease (56.8%). Procedures performed were 16 vertical band gastroplasties, 43 open gastric bypasses, 52 laparoscopic gastric bypasses, and 35 laparoscopic adjustable gastric bands.

Preoperative weight change was as follows: 31 patients gained weight (21.2%), 56 patients lost weight (38.3%), and 59 patients maintained their weight (40.4%).

While in women, there was no relationship between pre- and postoperative weight loss, men who gained weight preoperatively had significantly worse outcomes.

This study shows that while in women, ability to achieve a modest presurgical weight loss may not matter, in men inability to lose weight may predict poorer success.

Obviously, this study has methodological limitations and only included 23 men - perhaps not enough to make ruling statements about how men do with surgery.

Nevertheless, for now, our program continues to expect patients to demonstrate compliance with lifestyle changes including self-monitoring before considering anyone for bariatric surgery.

AMS
Edmonton, Alberta

IFSO Guidelines for Bariatric Centres

The International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO), at its Council Meeting in Porto, Portugal, September 2007, approved new guidelines for Bariatric Surgical Centres.

This not only reflects the global interest in this rapidly growing field of bariatric care, but also the need for guidelines that ensure at least a minimum standard of care for patients undergoing surgery for severe obesity.

The summary document, authored by John Melissas, IFSO President (2006-2007) and Head of the Bariatric Unit, at the University Hospital Heraklion, Greece, appears in this month's issue of OBESITY SURGERY.

While most of the recommendations make good sense - this document, not surprisingly, provides a view from the surgical perspective rather than providing a framework for overall bariatric care. There is no doubt that currently the surgeons have the upper hand in this discussion, given that the data increasingly supports the role of surgery as the most effective (if not only) treatment for severe obesity.

However, as I have blogged before, obesity surgery is not just about surgery!

The following are my comments on some of the IFSO recommendations:

"Ensure that individuals who provide services in the bariatric surgery program are adequately qualified to provide such services."

Fully agree, and would probably extend this recommendation to ANYONE dealing with bariatric patients - surgery or no surgery.

"Provide ancillary services such as specialized nursing care, dietary instruction, counseling, and psychological assistance if and when needed."

Another "no-brainer" - again, not only should these ancillary services be available, but health providers in these services should all have undergone basic training in bariatric care including sensitivity training and have at least a basic understanding of the nature of severe obesity, its complications and treatment.

"Have readily available consultants in cardiology, pulmonology, psychiatry, and rehabilitation with previous experience in treating bariatric surgery patients."

I would add to the list general internists, endocrinologists, gastroenterologists, intensivists, hospitalists, pharmacists and perhaps a few other specialities.

"Ensure that basic equipment necessary for the obese patients such as scales, operating room tables, instruments, and supplies specifically designed for bariatric laparoscopic and open surgery, laparoscopic towers, wheelchairs, various other articles of furniture, and lifts that can accommodate stretchers are available, as well as a recovery room capable of providing critical care to morbidly obese patients and an intensive care unit with similar capacity."

This should be an essential requirement for ANY hospital regularly admitting severely obese patients - unfortunately, this is now the case in virtually every hospital in the Western World.

"Have the complete line of necessary equipment, instruments, items of furniture, wheel chairs, operating room tables, beds, radiology facilities such as CT scan and other facilities specially designed and suitable for morbidly and super obese patients."

Same as above - should probably have such lists available in every hospital or medical facility in Canada.

"Have experienced interventional radiologists available to take over the non- surgical management of possible anastomotic leaks and strictures."

Good one! Sometimes these would be interventional gastroenterologists. As often some of these services can be urgently needed, it may not be enough to train only one individual to deal with these issues (travel, vacation, etc.). Obviously, radiology facilities for bariatric patients would be essential (see above).

"Has supervised support groups for bariatric patients."

I agree, support groups can be most helpful for these patients - but they do need supervision to not take off on "tangents".

"Provides lifetime follow-up for the majority and not less than 75% of all bariatric surgical patients."

Obviously, patients with bariatric surgery require life-long follow up - I only do not think that this is best done by the surgeon or "surgical" centres - in fact issues in follow-up are rarely surgical.

They are more often related to nutrition, rehabilitation and psychosocial issues that can ultimately determine outcome. Ideally counseling for these problems would be provided by primary care providers, who are adequately trained in looking after these patients - it is after all not "rocket science" - the majority of patients (if correctly selected prior to surgery) will probably do well with nutritional monitoring, regular lab work and access to psychosocial services as the need arises - all the job of primary care, not that of a surgeon.

Overall the IFSO recommendations are sensible and will hopefully be adopted by policy makers and health authorities in most countries, including Canada. Personally though, I prefer the route taken by the Canadian Association of Bariatric Physicians and Surgeons (CABPS), which ensures that ALL treatment options, both surgical and non-surgical find their place in the management of these complex patients - it is unlikely that surgeons will always provide the best "non-surgical" advise to their patients.

Obesity is indeed an ideal ground for fostering interprofessional practice.

AMS
Edmonton, Alberta

Obesity Can Make you Pee Your Pants

Not a very pleasant picture: wetting your pants every time you laugh, sneeze, lift a heavy load, exercise, drink too much coffee - the medical term for this common but rarely talked about problem is urinary incontinence.

For anatomical reasons, this problem (the involuntary leakage of urine) is largely limited to women.

Experts essentially speak of three common types of incontinence (there are others):

1) Stress incontinence: loss of small amounts of urine with coughing, laughing, sneezing, exercising or other movements that increase intraabdominal pressure and thus increase pressure on the bladder.

2) Urge incontinence: involuntary loss of urine often due to (nervous) overactivity of the bladder resulting in the sudden need or urge to urinate, sometimes after drinking a glass of water or even hearing the sound of running water.

3) Mixed incontinence: as the name says - when aspects of both forms of incontinence are present.

Obesity can not only increase the risk for urinary incontinence but also makes it worse in people who have it for other reasons (e.g. after childbirth).

So how strong is the link between urinary incontinence and obesity?

This was the question asked by Townsend and colleagues from Harvard in a recent article pulbished in OBESITY.

The researchers examined the associations of BMI and waist circumference with new-onset urinary incontinence among women aged 54-79 years in the Nurses' Health Study. From 2000 to 2002, they identified 6,790 women who reported at least monthly episodes of incontinence among 35,754 women reporting no UI in 2000. They also looked at the type of incontinence in individuals who had at least weekly incontinence.

There were highly significant trends of increasing risk of urinary incontinence with increasing BMI and waist circumferenc. Women with a BMI>35 were around 70% more likely to have incontinence compared to women with BMI 21-22.9.

Interestingly, while BMI was associated with urge and mixed, but not stress incontinence, waist circumference was associated only with stress urinary incontinence.

Fortunately, urinary incontinence is a very treatable condition, whereby, when present, obesity treatment can have a significant benefit.

As I have noted before - obesity affects virtually every organ system. The distress of having obesity-related urinary incontinence can far outweigh the "inconvenience" of having high blood pressure or dyslipidemia.

Always important to remember, obesity is not just about the heart!

AMS
Edmonton, Alberta

Lifestyle not a Determinant of Obesity in Teens?

Now here is a counter intuitive finding from Catherine Sabiston, of McGill University, and P.R.E. Crocker, of the University of British Columbia (UBC) published in the Journal of Adolescent Health earlier this year.

In their study of 900 Vancouver-area 16-18 year-old teenagers in Grades 10 through 12, neither was there a link between body mass index (BMI) values and levels of physical activity nor did the physically active teens eat a markedly healthier diet than their less-active counterparts.

If anything, the heavier teens were actually the ones making healthier food choices while the teens with “healthier” BMI values were no more likely to be physically active than those with higher, “unhealthier” values.

According to Dr. Sabiston (quoted in a press release from McGill University)

“A lot of people are surprised, but when you think about it, BMI doesn’t have a huge impact on physical activity. And in terms of diet, it actually makes sense that someone who is not happy with their body might try to eat more healthily. What this study really says, is that one cannot assume that someone who is physically active necessarily eats a healthy diet – or the reverse, that someone who is more sedentary or has a high BMI by definition eats a diet of junk food."

To me the findings aren't all that surprising. I have always maintained that health cannot be simply deducted from the number on your scale and that for every overweight kid who eats mostly junk food and spends every spare minute on his Xbox, there's a skinny kid out there who's no better.

The simple truth is that eating healthy and exercising is important at any weight!

On the other hand, just as simply eating poorly and not exercising by no means guarantees weight gain - simply eating healthy and exercising does not guarantee a so-called "healthy" weight.

When everyone eats too much and no one moves, it's likely the poor kids with the "wrong" genes that pack on the pounds - the kids with the "right" genes are simply lucky and can apparently get away with their lousy lifestyles - who says life has to be fair!

Of course, the words "wrong" and "right" in the previous sentence refer to these genes in today's world. Until not all too long ago in the history of mankind, the "wrong" genes would have been just "right" and vice versa (talking of thinking in circles).

AMS
Edmonton, Alberta

[Hat tip to Michael Dwyer of CIHR for sending me the McGill press release]