Sunday, May 24, 2015

Don't Displace Useful Advice with Useless Advice

In my opinion, our society has a very depressing narrative on chronic disease, one which is best characterised as hopelessness (blog).  But academics, doctors and people in public health also have their own equally demoralising narrative, which is that people don’t either adopt or stick to healthy lifestyle habits (which is probably a major reason for the emphasis on drugs over diet and lifestyle).  While I can understand and empathise with both points of view, I don’t think either is correct
  
The Risk of Coronary Heart Disease can be Massively Reduced

A review of observational studies found that a ‘healthy lifestyle’ is associated with an approximately 80% reduction in the incidence of first heat attacks (‘primary myocardial infarction’).  The criteria for a ‘healthy lifestyle’ (and the reduction in risk) varies from study to study, but often includes: a healthy diet*, lack of smoking, leisure-time physical activity, moderate alcohol intake, normal body weight, and normal cholesterol and blood pressure [1].  The magnitude of lower risk is consistent with the much lower incidence of CHD in in the industrialised counties at the beginning of the 20th century [2], the reduced risk of CHD in certain multifactorial diet intervention studies (such as the Lyon Diet Heart Study [3]) and the near absence of CHD or CHD risk factors among modern day hunter-gatherers and traditional cultures [4] [5]

* What a ‘healthy diet’ is isn’t defined in this review, though it’s likely to be similar to conventional nutrition recommendations and so may score people on how well they meet the food groups and their intake of SFA, salt and processed foods.  Whether this is the best measure is debatable, but

The Public can make Substantial Changes in Diet and Lifestyle

While only a small number of people tick all the boxes of a ‘healthy lifestyle’ (as defined in the studies cited by [1]), there is evidence that the general public can make substantial changes in their diet and lifestyle.  Smoking is a good example of this, where its prevalence in Australia and the US has decreased substantially (particularly among men*) in the last 50-60 years [6] [7].  Another example is that we reduced our intake of SFA (% of total calories) by about a third in the last ~50-60 years in response to response to dietary recommendations to do so (blog)


* I didn’t appreciate earlier how much of a gender disparity there was in smoking in the mid-20th century.  Perhaps this is what led to people almost exclusively testing the diet heart hypothesis only in men (blog), as much fewer women were smoking and therefore may have had a much lower incidence of CHD.  Also, just by looking at these statistics alone, it’s not surprising that age-adjusted CHD mortality has fallen over the last ~50-60 years

Willpower and Decision Fatigue

Altogether this suggests that one’s risk for CHD can be brought very low through the implementation of a big picture approach to diet and lifestyle that encompasses many elements, and that the general public can make significant changes to their diet and lifestyle, but most have plenty of room for improvement.  In this context, is it wise to promote replacing SFA with PUFA based on speculations regarding cholesterol levels when the evidence from ‘adequately controlled’ clinical trials suggests there’s no benefit of doing so?  Could this (most likely) useless dietary advice displace the delivery of and/or adherence to useful dietary/lifestyle advice?

There isn’t much direct research on how adherence to one aspect of a healthy lifestyle effects adherence to other aspects (the healthy user effect doesn’t count).  One study (experimental) found that withholding from tempting snack food or exerting other forms of self-control led to an increased consumption of ice cream (and in another instance, worse performance on a cognitive task) [8].  This is consistent with the concepts of ego depletion (willpower/self-regulation being a limited resource) [9] and decision fatigue (worse decision making over time) [10] [11].  That study and those concepts would all suggest that adherence to other aspects of a healthy lifestyle is likely to be worse.  Therefore, it should be more productive to initially base lifestyle recommendations on addressing the big picture and to ignore things of questionable clinical relevance (of which I would place replacing SFA with PUFA, as well as a number of other things such as the glycemic index for weight and metabolic health, salt for blood pressure, etc) 

Lastly, on a somewhat related note, some doctors have suggested that statins give people an illusion of protection, leading patients to make unhealthy lifestyle choices because of the thought that the statin will protect them or offset unhealthy decisions [12].  While I didn’t find any research on this (the article doesn’t seem to be based on a peer reviewed paper), it’s quite likely that it happens, at least in some people, and is another reason to not recommend potentially useless advice

2 comments:

  1. I've been looking at the mortality trends graphs for developed countries. A good place to start is coronary heart disease, middle age. Use this link for Mortality Trends as it sidesteps the annoying way that the main website linked is hacked by an advert at the moment; http://www.mortality-trends.org/specify.php?place=gbr&cod=vch&age=35-69&submit=Go

    Now the funny thing is that all of these countries that are Westernised, including Japan (but not the Eastern Bloc countries), have pretty much the same "tipping point" date, which is around 1972, after which CHD mortality nose-dives spectacularly.
    How does this correlate? PUFA probably began to increase globally after this date, but only slowly. 1972 is the year margarine became legal in NZ, for example.
    However, saturated fat intake in Japan doubled from 1965-1975, to 16g/day, and cholesterol increased accordingly. This is doubly important because Japan was one of the very low SFA, low cholesterol, low CHD societies used to support the "you're just not going low enough yet" defense of the diet-heart hypothesis.
    Smoking has declined, but Japan still has a higher rate than the US. The turning point was the mid-70s. Women have a low rate of smoking with little change.
    Pollution - Japanese air pollution legislation dates from 1967-1971 and can be taken as a marker for awareness in general; these dates are typical of the developed world (but not the Eastern Bloc). Early legislation was weak but accompanied by a great deal of publicity about what constituted a healthy environment and workplace, so individual action might have provided the vanguard effect.
    Nutrition - when did we start being able to eat fresh food out of season? Variety of diet and better micronutrition - through importation from soils supplying minerals lacking at home, and improved animal feeds - are definitely trends that match the CHD decline - PUFA can be seen as just one aspect of this. Food fortification increased and the modern cult of vitamins and what are now known as superfoods (but were then called molasses, wheatgerm and yeast) dates from this period.

    CHD mortality trails off towards the end of the first period in history where almost everyone had enough to eat. The story isn't usually told like that, of course.

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    1. The consistency of those trends is quite interesting, and as you say, the trends in Japan are quite a powerful contradiction of the diet heart hypothesis. It’s difficult to understand why CHD mortality declined because so many factors can be involved, but you’re making a good case for air pollution being a very important factor.

      Regarding historical trends, I don’t think it should necessarily be assumed that it takes decades for things to have an effect, as some of the trials, particularly Oslo, Finnish and Lyon all show that you can have a large effect on CHD mortality in only a few years.

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