BMI Poor Measure of Body Fat in Heart Failure
Body mass index (BMI) is a widely used anthropmetric surrogate for body composition as it correlates well with body fat content across a wide range of body ages, shapes, and sizes.
However it does have its limitations in special populations (e.g. infants, competitive athletes, pregnancy, etc.). It may now be time to add patients with heart failure to this list.
In a study just published by Antigone Oreopoulos and colleagues from the University of Alberta, Edmonton, Canada, in Congestive Heart Failure, we examined the relationship between various anthropometric indices and body composition in men and women with heart failure.
Body composition was assessed by dual-energy x-ray absorptiometry in 140 patients with congestive heart failure and compared to BMI, waist circumference, waist-stature ratio, and waist index. Diagnostic accuracy of detecting obesity or high central fat was also examined.
While in men, all of the anthropometric indices except waist index were just as well (albeit moderately) correlated with lean body mass as with the actual percentage of body fat, in women, all 4 anthropometric measures were unable to significantly differentiate between body fat and lean body mass.
Thus, none of the anthropometric indices accurately reflected body composition in women with congestive heart failure and were also of limited use in men.
These finding may be due to the remarkable variability in lean body mass and fluid retention seen in these patients – both of which can strongly determine body weight irrespective of changes in body fat.
The implications for clinicians are to interpret anthropometric indices including BMI with caution in patients with heart failure – both with regard to predicting excess fat as well as in regard to any changes in body weight.
p.s. The Canadian Obesity Network is seeking a new Finance Manager. For more information click here.
Oreopoulos A, Fonarow GC, Ezekowitz JA, McAlister FA, Sharma AM, Kalantar-Zadeh K, Norris CM, Johnson JA, & Padwal RS (2011). Do Anthropometric Indices Accurately Reflect Directly Measured Body Composition in Men and Women With Chronic Heart Failure? Congestive heart failure (Greenwich, Conn.), 17 (2), 90-92 PMID: 21449998
Are Normal-Weight Americans Over-Fat?
Readers of these pages will recall that I am not a fan of defining obesity based on BMI because this measure of “fatness” does not perform well when applied to individuals. Thus, people with identical BMI levels can have remarkably different levels of body fat (not to mention remarkable differences in their actual health status).
This, incidentally, is also true for people with BMI levels in the so-called “normal” range, a finding which prompted Marie-Pierre St-Onge from Columbia University, New York, to ask whether normal-weight Americans are perhaps “over-fat” (rather than overweight). Her commentary was just published online in OBESITY.
it has previously been suggested that a normal body fat level should be around 21–32% for 21- to 39-year-old, normal-weight women and 8–20% for men of the same age and BMI category.
However, a recent analyses of data from National Health and Nutrition Examination Surveys (NHANES) 1999–2004, reported that the 5th percentile for body fat, which should represent the leanest of the US population, corresponds to 28 and 17% body fat for women and men, respectively.
Most disturbingly, the 50th percentile of body fat in the US population was as high as 41 and 28%, for women and men, respectively.
When categorized by BMI and age, the data also show high percent body fat values, particularly in lower BMI categories.
Thus, clearly, even normal-weight Americans appear to have more body fat than is considered “normal”.
This is an important finding, because “normal” BMI levels are generally interpreted as being “healthy”, meaning that no “weight-loss” intervention is recommended.
As I have pointed out before, BMI levels are limited in defining body-fat-related health, because an excess BMI alone does not necessarily reflect ill health.
On the other hand, it now seems that a normal BMI level does not necessarily reflect good health either, as a substantial number of people with normal BMI levels may well have excess body fat, which can potentially contribute to cardiometabolic and other “body-fat-related” health problems.
Perhaps, it is time for clinicians to turn to more accurate measures of body-composition when defining obesity rather than simply using the rather crude surrogate of BMI.
St-Onge MP (2010). Are normal-weight americans over-fat? Obesity (Silver Spring, Md.), 18 (11), 2067-8 PMID: 20978478
Li C, Ford ES, Zhao G, Balluz LS, & Giles WH (2009). Estimates of body composition with dual-energy X-ray absorptiometry in adults. The American journal of clinical nutrition, 90 (6), 1457-65 PMID: 19812179
How Lack of Sleep Wrecks Your Diet
Regular readers will recall the many previous posts on the relationship between lack of sleep and weight gain. Now new evidence shows that lack of adequate sleep may be even more detrimental in anyone trying to lose weight.
In a study published in a recent issue of the Annals of Internal Medicine, Arlet Nedeltcheva and colleagues from the University of Chicago, tested the hypothesis that lack of sufficient sleep adversely affects the neuroendocrine response and metabolic effects of caloric restriction.
In a complicated randomised, 2-period, 2-condition crossover study, 10 overweight nonsmoking adults (3 women and 7 men) with a mean age of 41 years and a BMI around 27, were subjected to 14 days of moderate caloric restriction with 8.5 or 5.5 hours of nighttime sleep in a sleep laboratory.
Despite the same amount of caloric restriction, sleep deprivations resulted in 55% less fat loss and alarmingly increased the loss of fat-free mass (muscle) by almost 60%.
Sleep deprivation was also associated with increased hunger and reduced fat oxidation.
The authors conclude that adequate sleep is important to prevent the loss of fat-free mass during weight loss.
As a corollary to this, we can perhaps also conclude that trying to lose weight during times of sleep deprivation may be counterproductive in that it is more likely to lead to loss of lean tissue than get rid of the unwanted fat.
I have often advised my time-pressed patients that if they had to chose between 60 mins of exercise and 60 mins of sleep to go for the sleep. This is particularly true, as we know that exercise further increases the need for sleep thereby, making the degree of sleep deprivation, which many of my patients already face, even worse.
I propose that a careful sleep history (if not a formal sleep study) and sleep counseling should be part of every bariatric assessment and weight management plan.
You can now also follow me and post your comments on Facebook
Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, & Penev PD (2010). Insufficient sleep undermines dietary efforts to reduce adiposity. Annals of internal medicine, 153 (7), 435-41 PMID: 20921542
Will Exercise Make You Fat?
Yesterday, I had the pleasure of hosting John Blundell, at the Research in Progress seminar series at the Alberta Diabetes Institute.
Dr. Blundell is Professor of bio-psychology at the University of Leeds, UK, and is certainly one of the preeminent authorities on the bio-psychology of ingestive behaviour.
His presentation with the rather provocative title, “Will exercise make you fat?”, started with a broadside at the media, which lately has been quite active in promoting this notion.
However, as Blundell pointed out, this simplistic message is far from accurate in that the relationship between physical activity and its impact on ingestive behaviour and body weight is anything but straightforward.
For one, although short-term studies (days) do often show an increase in appetite, this is by no means regularly observed in longer-term studies (weeks).
In a paper he recently published in the Journal of Clinical Endocrinology and Metabolism, Blundell recently examined the effects of medium-term exercise on fasting and post-prandial levels of appetite-related hormones and subjective appetite sensations in overweight and obese individuals.
The study included 22 sedentary individuals who took part in a 12-wk supervised exercise programme (five times per week, 75% maximal heart rate) and were requested not to change their food intake during the study.
Not only did exercise result in a significant, albeit modest (~3 Kg), reduction in body weight and fasting insulin and an increase in ghrelin plasma levels but also in a reduction in fasting hunger sensations.
A significant reduction in postprandial insulin plasma levels and a tendency toward an increase in the delayed release of glucagon-like peptide-1 (90-180 min) and a greater suppression of postprandial ghrelin.
Thus, although exercise-induced weight loss was associated with physiological and biopsychological changes towards an increased drive to eat in the fasting state, this compensatory effect seems to be balanced by an improved satiety response to a meal and improved sensitivity of the appetite control system.
However, as Blundell pointed out, these mean changes hide the immense diversity between individuals.
Based on these studies it appears impossible to predict in advance how individuals will respond: Some people, in response to exercise, will be hungry and may overeat – others may find that they are much better in controlling their food intake.
Importantly, all subjects, irrespective of their body weight, showed a reduction in their amount of body fat and improvements in risk markers like physical fitness and blood pressure.
Thus, Blundell concludes, exercise does reduce body fat (even in people who do not lose weight) and has beneficial effects on important health parameters.
The answer therefore clearly is: no, exercise does not make you fat, but don’t expect to lose a lot of weight.
The many important benefits of exercise can, unfortunately, not be measured on a scale.
Martins C, Kulseng B, King NA, Holst JJ, & Blundell JE (2010). The effects of exercise-induced weight loss on appetite-related peptides and motivation to eat. The Journal of clinical endocrinology and metabolism, 95 (4), 1609-16 PMID: 20150577
Do Obese People Need More Drugs?
Of course, obesity is associated with a wide range of health problems like high blood pressure, diabetes, arthritis, or reflux disease, all of which may all require pharmacological treatment. But this is not what this post is about.
Rather, this post is actually about the question whether or not larger patients need higher doses of medications to have an optimal treatment effect.
This topic was recently discussed by Matthew Falagas and Drosos Karageorgopoulos in a Lancet article that specifically addresses the issue of dose adjustments for antimicrobial agents in larger patients.
As the authors point out, body size is routinely considered in the optimization of drug therapy in oncology, anaesthetics and pediatrics. However, there remains a paucity of data on the optimal dosing of pharmacological agents for most of the drugs we use in clinical practice.
Thus, although regulatory agencies regularly demand special pharmacokinetic studies in children, elderly prople and patients with renal or hepatic impairment, no such studies are demanded for obese or even severely obese patients.
Requiring such studies would at least make theoretical sense as, conceivably, obesity can affect drug absorption, distribution, metabolism and clearance. Furthermore, it is obvious that body composition can particularly affect the disposition of lipophilic compounds. Obese patients are also likely to have comorbiditiesthat can affect these parameters (e.g. fatty liver disease) and are much more likely to be on multiple medications that can make drug-drug interactions problematic.
In short, as pointed out by Falgas and Karageorgopoulos the one-size-fits-all strategy for antimicrobial agents (and other drugs?) may well be outdated and require much more consideration than has been given to this issue in the past.