Tuesday, January 13, 2015

The US News Diet Rankings: Part 2

Health Risks

Are there health risks?
Possibly. By shunning dairy and grains, you’re at risk of missing out on a lot of nutrients. Also, if you’re not careful about making lean meat choices, you’ll quickly ratchet up your risk for heart problems.
While there are no specific dieter restrictions, you’ll want to consider talking with your doctor before making changes to your meal plans.

Calcium is probably the only nutrient in a Paleo diet* where the intake won’t meet the RDI because of the lack of dairy (meanwhile conventional dietary advice is often low in choline).  There are really no other nutrients in dairy and grains that can’t be found in meat, fruit and vegetables, which is generally true of most foods.  For example, despite people describing whole grains as good sources of B vitamins, meat is actually a better source of most of the B vitamins [1].

In the Paleo RCTs the Paleo diet is more nutrient dense than conventional dietary advice, which is not surprising considering that meat, fruit and vegetables is more nutrient dense per calorie than grains and dairy.

      Nutrient intake (% of RDA)                  Nutrient intake (% of RDA)**
      Average: PD 173%, DHCG 117%        Average: PD 196%, ADA 141%
      Median: PD 143%, DHCG 118%         Median: PD 156%, ADA 137%

As for calcium, there are other factors of a Paleo diet that probably makes up for the lower intake of calcium:

  • Vitamin D increases calcium absorption, and sunlight (or vitamin D supplements for those in higher latitudes) is widely recommended in the Paleo community
  • At most calcium/calcium + vitamin D supplementation reduces fracture rates by 24% [2], while vitamin K2 supplementation reduces fracture rates by 60% [3].  Conventional dietary advice recommends reducing animal fat, which probably explains how vitamin K2 is far more successful than calcium (the nutrient most of us are lacking for bone health is probably vitamin K2, not calcium)
  • By reducing grains and legumes, Paleo diets have a lower amount of phytic acid (which reduces calcium absorption) 

Lastly as for SFA and CVD, observational studies find no benefit when SFA is replaced with MUFA or carbohydrate [4] [5], and while replacing SFA with PUFA is associated with reduced CHD in observational studies [4], in the better controlled RCTs replacing SFA with PUFA results in either: lower CHD events, but not CHD mortality and total mortality [6] [7]; or higher CHD events and total mortality [7] [8] [9]

* Unless someone often regularly includes bulletproof coffee, ‘Paleo’ junk food or huge amounts of added fat in their Paleo diet, in which case all of those things would replace nutrient dense foods, thereby reducing nutrient intake.  There are bad implementations of all diets

** Nutrient intake adjusted to 2000kcal.  ‘RDA’ used came from average of men and women Australian DRI

*** In the section below they say the macronutrient ratio (P:F:C) of “a sample Paleo menu” is 38:39:23.  I don’t know where they got those figures from and I’m not too keen on 38% of calories from protein.  Cordain, et al estimated hunter-gatherers got 19-35% of calories from protein 28-48% from fat and 22-40% from carbohydrate, which averages to 27:43:31 (I know, it equals 101%)

Rankings

The first page is what you expect, a whole bunch of diets which conform to dietary guidelines, with a little variation.  Page two is where you start to see some wacky diets with gimmicks, dubious claims and/or meal replacements.  Paleo was equal last with the Dukan diet and beating Paleo was:

  • Other diets that restricted food groups like the vegetarian diet #11 and the vegan diet #19.  Because restricting food groups is bad when it’s grains, but is fine when it’s meat or all animal foods (which do have unique nutrient profile unlike grains)
  • Diets based on dubious weight loss claims or outrageous justifications such as the Flat Belly Diet #16, Abs Diet #19, Medifast Diet #26, Acid-Alkaline diet #28, the Supercharged Hormone Diet #28 and Body Reset Diet #30

The rankings lose all credibility with their fairly high ranking of Slim-Fast #13, a diet based on poor quality, highly refined meal replacements.  Slim-Fast ranks more highly than several other diets based on food such as Zone #23 and Low GI #24 and is equal #13 with the Anti-Inflammatory diet


I’ve noticed a few things on how diets get a high rank:

  • Conform to the dietary guidelines, regarding macronutrient ratios and food groups (ignore that food groups are largely a human construct and often have little to do with nutrient profiles)
  • Emphasise the importance of reducing SFA, salt and dietary cholesterol (ignore that there’s no good evidence for this)
  • Only bother doing research if you followed the previous two points, otherwise it won’t count for much and probably won’t get cited anyway.  Even if you have no research supporting your diet you can piggyback on other people’s research and say that your diet is similar to theirs
  • Promote weight loss myths that the authors believe such as eating 6 small meals a day
  • Your diet should have lots of handholding.  Meal replacements or delivering meals is preferable to your dieters having to shop and cook their own food.  And certainly don’t require that your dieters have to do something crazy like research the diet to understand it
  • Your diet should be flexible so that it’s sustainable and easy to follow (ignore that mediocre effort often just produces mediocre results).  Diets that do enough to actually be effective are definitely unsustainable and there’s no way your dieters will stick with it long term
  • Leading on from the previous point, for the long term weight loss criteria your diet’s delivered meals or meal replacements should create a minor calorie deficit like 20 calories a day, not to be that effective [10], but just to tick boxes in the rankings.

To wrap up, a positive is that I don’t expect I’ll need to respond to the rankings again.  If history is anything to go by, the rankings and their justifications won’t change that much, even with new evidence.

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