Lancet confirms fat is bad

Earlier this week, the prestigious medical journal The Lancet published an article about the health effects of obesity [1].

Spoiler alert – obesity kills you.

That sounds a lot like old news.  Why is a leading medical journal wasting space printing studies that tell us what we already know?  Well, up until now, the answer wasn’t as settled as people might have thought.

From the earliest writings of the ancient Greeks, fat people were always considered weak-willed or morally lacking.  Obese people either over-indulged or were lazy sods that deserved the indignation of the clearly morally superior skinny people.  Medical science initially seemed to back up that notion with hard data.  Body Mass Index (or BMI, your weight in kilograms divided by your height in metres squared) between 20 and 25 was the ultimate goal, and if you were above that, you were set to live a shorter and unhappier life.

Then a few years ago, a few studies came out showing that being overweight wasn’t as dire as people thought, and in fact, some studies showed that being overweight and mildly obese offered a small survival advantage over a weight in the “normal” range [2].  This was known as the obesity paradox.

So questions hung in the air like the sickly sweet smell of freshly baked donuts – Did the medical community get obesity wrong?  Were we meant to be cuddly instead of bony?  Were the lard nazi’s tricking us into lifestyles of kale and sit ups under false pretences?

The study by the objectively named Global BMI Mortality Collaboration seems to have definitively answered those questions.  The Global BMI Mortality Collaboration was a collective effort of more than 500 researchers from more than 32 countries, who pooled the resources of 239 different studies involving more than 10 million adults.  The collaborators weeded out more than 6 million people to form a group of 3,951,455 people who had never smoked and had not been diagnosed with a chronic disease before being recruited, and who had survived for more than 5 years after being recruited.  This made their group of participants in this study as statistically robust as possible.  These participants were followed for about 14 years.  Overall, 385,879 of them died.  To see whether obesity had an impact on mortality, they adjusted the raw numbers for age and gender, and calculated the likelihood of a participant dying depending in their BMI.

It isn’t good news for those of us who are of ample proportion.  Compared to those in the healthiest weight range, the most obese had a two-and-half times greater risk of dying from any cause.  Those who were overweight but not obese, which the previous studies suggested may have been ok, had an increased risk of dying too, but only by about 7%.  Obese males had a higher risk of dying than obese females, and obesity was worse for you if you were obese and young rather than obese and old.  Though before all the skinny people start skiting, those with a BMI of under 20 also had a higher mortality.  The best place to be was with a BMI of 20-25.

 

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Statistically speaking, this is a really strong study, so the conclusions it draws are hard to argue with.  It confirms that the BMI of 20-25 is the ideal weight, and that either extreme of body weight is certainly undesirable.

There are a couple of things to note.  Firstly, being overweight still isn’t that bad.  Sure, it’s not ideal like the older studies may have said, but a 7% increase in all-cause mortality isn’t going to particularly cut your life short.  So don’t panic about your love handles just yet.

Secondly, despite the statistical power of this study, it really only answers the single question: Is obesity related to mortality?  It answers it, and it answers it conclusively, but it doesn’t tell us how or why obesity and mortality are related, which are more important questions overall.

Because while it’s necessary to know that obesity, illness and death are related, knowing how they are related can then help us understand the why of obesity, which will then help doctors give patients real information that they can use.

For example, the Lancet study didn’t look at causation.  Is it that obesity causes chronic diseases which then cause early mortality like is the case with smoking?  Or is it that there’s another cause underlying both obesity and chronic disease, with obesity being unfairly framed in a guilt-by-association way?

Obesity Guilty Framed

What about mitigating factors?  If you’re fat but you’re also very fit, what’s your mortality then?  If you have a gastric bypass or a gastric sleeve and you shed a hundred pounds, does your mortality improve?  I’ll try and answer some of these question in future blogs.

Like all good research, this study in The Lancet seems to have generated more questions than answers.  What’s certain is that more research needs to be done.

If you are obese and you are concerned about your health, then talk to your GP or dietician.  Be sensible with your health.  Sure, obesity isn’t great, but you can sometimes do as much damage to yourself through poorly designed weight loss programs than you can with a dozen donuts.

References
[1]        Global BMI Mortality Collaboration. Body-mass index and all-cause mortality: individual participant data meta-analysis of 239 prospective studies in four continents. Lancet 2016 13 july 2016.
[2]        Flegal KM, Kit BK, Orpana H, Graubard BI. Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA : the journal of the American Medical Association 2013 Jan 2;309(1):71-82.

Dr Caroline Leaf and the obesity overstatement

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Caroline Leaf is on the nutritional warpath.

Our society isn’t the best when it comes to eating right. Fast food and junk food are more attractive options than fresh food, and nearly everyone knows it. Today, the internet is flooded with celebrity chefs and self-titled experts attempting to leverage some profit by advocating their own brand of diet or herb as the simple solution to what is a deceptively complex problem.

Dr Caroline Leaf is a communication pathologist and self-titled cognitive neuroscientist. In recent times she has also jumped on to the nutritional bandwagon, advocating organic gluten free recipes through food-selfies, and reposting Jamie Oliver quotes.

Today’s meme follows a similar line, where she has reposted an image which fits with her personal cognitive bias – a picture of french-fries in a cigarette packet, accompanied by the tag line, “THE OBESITY DEATH RATE IS OVERTAKING CIGARETTE SMOKING. Consume with caution”.

The image is a case study in overstatement. According to the most recent Global Burden of Disease data (currently 2010), the death rate associated with cigarette smoking is currently 91.4 per 100,000 population while the death rate associated with a high BMI is only 48.1 per 100,000 population. Even extrapolating the figures to the current year, the predicted rates would still be 89.1 vs 51.9 respectively, which are still a long way apart. On the current trends, obesity won’t overtake smoking as a global cause of death until 2055. So saying the obesity death rate is overtaking cigarette smoking is like saying that Christmas is coming – it’s technically true, but it’s still a long way off.

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There are a couple of reasons why deaths associated with obesity are rising while the deaths associated with cigarette smoking are falling. The most obvious is that cigarette smoking is decreasing, but treatments for smoking related illnesses are also concurrently improving, so less people are getting sick from cigarette smoking and those that do are less likely to die.

Of course, it’s no secret that more people, especially in the western world, are getting fatter. The old assumption was that obesity contributed to metabolic syndrome which then caused heart disease and type 2 diabetes and a concomitant rise in deaths. However, new evidence casts serious doubt over these assumptions.

In a meta-analysis of the association of mortality to BMI, Flegal, Kit, Orpana, and Graubard (2013) showed that overweight people have a slightly lower death rate than normal weight people, those with mild obesity have the same risk of death as normal weight people, and that the overall risk of all classes of obesity was small (relative risk 1.18 (95% CI, 1.12-1.25)). As a comparison, the risk of death from cigarette smoking is up to 2.66 (Shavelle, Paculdo, Strauss, & Kush, 2008)**.

The key to understanding this paradox is found in another meta-analysis, by Kramer, Zinman, and Retnakaran (2013) They showed that obesity and metabolic dysfunction are separate entities, with metabolically healthy obese people having the same risk of death as metabolically healthy people of normal weight (RR 1.19 (95% CI 0.98 to 1.38)) while metabolically unhealthy people with a normal weight had a risk three times that (RR 3.14 (95% CI, 2.36 to 3.93)).

So the key isn’t whether someone’s obese or not, the key is whether someone’s metabolically healthy or not (which is another blog for another time). According to the latest scientific evidence, the obesity death rate probably isn’t related to obesity after all.

Dr Leaf might be on the nutritional warpath with the right intentions, but her lack of expertise and willingness to fact-check is showing with every meme. If she wants to continue portraying herself as an expert in the area of food and nutrition, she needs to move away from her personal biases and start promoting proper science.

References

Flegal, K. M., Kit, B. K., Orpana, H., & Graubard, B. I. (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA, 309(1), 71-82. doi: 10.1001/jama.2012.113905

Kramer, C. K., Zinman, B., & Retnakaran, R. (2013). Are metabolically healthy overweight and obesity benign conditions?: A systematic review and meta-analysis. Ann Intern Med, 159(11), 758-769. doi: 10.7326/0003-4819-159-11-201312030-00008

Shavelle, R. M., Paculdo, D. R., Strauss, D. J., & Kush, S. J. (2008). Smoking habit and mortality: a meta-analysis. J Insur Med, 40(3-4), 170-178.

Graph data: Institute for Health Metrics and Evaluation (IHME). GBD Database. Seattle, WA: IHME, University of Washington, 2014. Available from http://www.healthdata.org/search-gbd-data. Accessed 15/1/2015

** This means that a smoker is more than twice as likely to die compared to a non-smoker, but an obese person’s risk is only about one fifth more likely to die compared to a person with a normal body mass index.