Sunday, January 11, 2015

The US News Diet Rankings: Part 1

The annual circus of the US News Diet Rankings is back for a repeat performance this year.  Not one to disappoint old fans, they’re performing almost the exact same act as last year.  I usually don’t deal with comedy on this blog and leave that kind of thing to The Onion.  But I’m writing about this today because some poor person might get the idea that the rankings are supported by evidence and logic, and not simply written by clowns.

In this post I’ll be discussing their representation of the research regarding the Paleo diet (see here).  In the next post I’ll discuss the rest and look where some of the diets were ranked.

There are now 4 trials comparing the Paleo diet to convention dietary advice:

·         Lindeberg, et al (2009).  Paleo vs. Mediterranean
·         Jonnson, et al (2009).  Paleo vs. American Diabetes Association
·         Mellberg, et al (2014).  Paleo vs. Nordic Nutrition Recommendations
·         Boers, et al (2014).  Paleo vs. Dutch Health Council Guidelines

There are also 4 uncontrolled Paleo trials which I won’t discuss here besides saying that the first 3 were positive and the last one was a mix, but had some issues (see here)

·         Osterdahl, et al (2007)
·         Frassetto, et al (2009)
·         Ryberg, et al (2013)
·         Smith, et al (2014)

Weight Loss

“Will you lose weight?”
“No way to tell. Paleo diets haven’t yet drawn the attention of many researchers. One tiny study that looked at weight loss found that 14 participants lost an average of about 5 pounds after three weeks on a Paleo regimen. (But even the researchers called their study “underpowered.”) Still, if you build a “calorie deficit” into your Paleo plan – eating fewer calories than your daily recommended max, or burning off extra by exercising – you should shed some pounds. How quickly and whether you keep them off is up to you.”



Paleo
Other Group
P value between groups
Lindeberg
(12 weeks)
Δ Weight (kg)
-5.0
-3.8
0.30
Δ Waist (cm)
-5.6
-2.9
0.03
Δ Fat mass (%)
-2.6
-1.6
0.30
Jonnson
(3 months)*
BMI
28
29
0.04
Waist (cm)
94
98
0.02
Mellberg
(24 months)
Δ Weight (kg)
-2.4
1.4
0.059
Δ Fat mass (kg)
-4.6
-2.9
0.095
Boers
(2 weeks)
Δ Weight (kg)
-2.7
-1.7
CI = (-2.3; -0.3)
Δ Waist (cm)
-3.1
-3.3
?
Bold: p < 0.05.  Underline: p = 0.05-0.10
* Jonnson, et al (2009) used a crossover design

The rankings mention the importance of a calorie deficit.  In the first three trials both groups spontaneously reduced calorie intake on both diets (both diets were ad libitum), though to a greater extent in the Paleo diet.  Satiety is often a limiting factor in weight loss using simple calorie restriction.  In the studies that measured satiety the Paleo diet has been found to be more satiating per calorie than the Mediterranean diet [1] and the American Diabetes Association diet [2]

The rankings misrepresent the literature on Paleo diets regarding weight loss.  They only reference one uncontrolled trial and none the four RCTs, which found: (1) you probably will lose weight on the Paleo diet; (2) the Paleo diet is equal to or better than conventional dietary advice for weight loss (etc); and (3) the Paleo diet is more satiating per calorie than conventional dietary advice

* The Boers study was different as it maintained set calorie intakes and the diets were made isocaloric

Cardiovascular Disease

“Does it have cardiovascular benefits?”
“Unknown. While some studies have linked Paleo diets with reducing blood pressure, bad “LDL” cholesterol and triglycerides (a fatty substance that can raise heart disease risk), they have been few, small and short. And all that fat would worry most experts.”



Paleo
Other Group
P value between groups
Jonnson
(3 months)*
HDL-C
1.34
1.26
0.03
LDL-C
2.7
2.8
0.5
Triglycerides
1.0
1.5
0.003
SBP
140
149
0.13
DBP
79
83
0.03
Mellberg
(24 months)
Δ HDL-C
0.16
0.18
0.896
Δ LDL-C
-0.26
-0.07
0.291
Δ Triglycerides
-0.23
-0.01
0.001
Δ SBP
-3.7
1.7
0.293
Δ DBP
-4.8
-1.5
0.349
Boers
(2 weeks)**
Δ total-C:HDL-C
-0.54
0.47
0.03
Δ Triglycerides
-0.9
0.1
0.00
Δ SBP
-9
-5
0.04
Δ DBP
-8
-3
0.09
Bold: p < 0.05.  Underline: p = 0.05-0.10
* Jonnson, et al (2009) used a crossover design
** P value after adjustment for weight loss

I would argue that the cardiovascular benefits of almost every diet ranked is unknown without long term RCTs measuring CVD events, CVD mortality and total mortality, but I’ll settle for risk factors.

Three of the controlled trials found that: (1) the Paleo diet improves blood pressure and blood lipids; and (2) the Paleo diet is equal to or better than conventional dietary advice for improving blood pressure and blood lipids.

The statement “and all that fat would worry most experts” is among the more idiotic.  Why would they be worried about a higher fat diet?  Current evidence doesn’t support higher fat being an issue for CVD or low fat diets being therapeutic.  Isocaloric replacement of carbohydrate with any fat reduces the total-C:HDL-C ratio [3], the best predictor of CHD [4].  In observational studies, total fat [5] or replacing SFA with carbohydrate has no effect on CHD risk [6] [7].  Clinical trials have found that low fat diets don’t reduce CHD [8] [9], and just to make a point: the low fat, low SFA diet in the WHI, which included more fruits and vegetables, increased the incidence of CVD events among women with pre-existing CVD (HR=1.26, CI=1.03-1.54, P<0.006) [9].  Besides, the Mediterranean diet is ~35-40% of calories from fat and Cordain, et al estimate ~28-58% of calories came from fat in hunter-gatherer diets (average of 28% and 58% = 43%) [10].  Do you think a few % of calories from fat makes a difference?  If not, no double standards please.

Diabetes

Can it prevent or control diabetes?
Unknown.
Prevention: Being overweight is one of the biggest risk factors for Type 2 diabetes. If reverting back to the Paleo era helps you lose weight and keep it off, you’ll stand a better chance of staving off the disease.
Control: One small study comparing a Paleo and a traditional diabetes diet in 13 Type 2 diabetics showed the Paleo diet resulted in lower levels of hemoglobin A1C, a measure of blood sugar over time. The approach needs to be studied more before strong conclusions can be drawn, but most diabetes experts recommend a diet that includes whole grains and dairy products.



Paleo
Other Group
P value between groups
Lindeberg
(12 weeks)
Δ HbA1c
-0.13
-0.03
0.4
Δ 30m glucose
-2.0
-0.4
0.008
Δ 120m glucose
-3.3
-0.9
0.003
Δ AUC glucose
-290
-80
0.001
Normal glucose levels***
14/14
7/15
0.0007
Diabetic glucose levels***
0/14
5/15
0.01
Δ HOMA-IR
-0.24
-0.19
0.7
Jonnson
(3 months)*
HbA1c
5.5
5.9
0.02
Fasting glucose
7.0
7.5
0.08
AUC glucose
1398
1478
0.2
HOMA IR
1.4
1.4
0.9
Diabetic OGTT (y/n)
8/5
9/4
1.0
Mellberg
(24 months)
Δ Fasting glucose
-0.04
-0.002
0.465
Δ Fasting insulin
-0.18
0.87
0.500
Boers
(2 weeks)**
Δ Fasting glucose
-0.4
-0.4
0.91
Δ Fasting insulin
-2.7
-1.4
0.44
Δ HOMA IR
-0.9
-0.5
0.41
Δ AUC glucose
-18
9
0.13
Δ AUC insulin
-1918
362
0.63
Bold: p < 0.05.  Underline: p = 0.05-0.10
* Jonnson, et al (2009) used a crossover design
** P value after adjustment for weight loss
*** No statistics on change from baseline within groups.  Paleo had 2 normal and 10 diabetic at baseline.  Mediterranean had 2 normal 9 diabetic at baseline

Weight loss is important regarding type 2 diabetes and as discussed in the first section the Paleo diet is good for weight loss, being equal to or better than conventional dietary advice.  These trials also provide a good example of how calorie intake/weight loss effects blood glucose:

·         The Lindeberg trial had more weight loss in both groups and a greater difference between the groups and consequently glucose tolerance improved and to a greater extent in the Paleo group
·         Compliance was poor in the Mellberg trial, which lead to only minor weight loss and little improvement in fasting glucose and insulin at 24 months
·         The Boers trial was isocaloric and when adjusted for weight loss there were no significant differences between the groups regarding glucose and insulin

But again the rankings only cite one trial when there are 4 controlled trials measuring glucose and insulin levels, and the one trial they cited wasn’t the more appropriate and very favourable Lindeberg trial.  Once again the controlled trials find that: (1) the Paleo diet can improve glucose levels and insulin resistance; (2) the Paleo diet is equal to or better than conventional dietary advice for improving glucose levels and insulin resistance; and (3) poor compliance = poor results, regardless of diet (the Mellberg trial)

Conclusion

The rankings consistently misrepresent the research regarding the Paleo RCTs, by citing inappropriate studies and only ever one study per section, making it seem like there’s less research on the Paleo diet than there is.  The Paleo RCTs find that the Paleo diet can promote weight loss and improve CVD risk factors, glucose levels and insulin sensitivity, and that the effect of the Paleo diet is equal to or better than conventional dietary advice.


I acknowledge that 4 RCTs with a total of 146 participants isn’t much and obviously isn’t enough justification to completely overhaul dietary guidelines, but the results of these trials should surely spark some interest and be replicated on a larger scale.

2 comments:

  1. with regards to the Melberg study

    CONCLUSIONS: A PD has greater beneficial effects vs an NNR diet regarding fat mass, abdominal obesity and triglyceride levels in
    obese postmenopausal women; effects not sustained for anthropometric measurements at 24 months. Adherence to protein intake was poor in the PD group. The long-term consequences of these changes remain to be studied.

    The PD provided
    30% of energy intake (E%) from protein, 40 E% fat and 30 E%
    carbohydrates and included a recommendation for a high intake of MUFA and polyunsaturated fatty acids (PUFA). The diet was based on lean meat, fish, eggs, vegetables, fruits, berries and nuts. Additional fat sources were avocado and oils (rapeseed and olive oil) used in food preparation and dressing. Dairy products, cereals, added salt and refined fats and sugar were excluded.
    The NNR diet12 was aiming at a daily intake of 15 E% protein, 25–30 E% fat and 55–60 E% carbohydrates, with emphasis on lowfat dairy products and high-fibre products.

    ReplyDelete
    Replies
    1. Hi Charles, I have read the Mellberg study. What point were you aiming to make?

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