Comments on: Mono-rich diets and heart disease prevention: the first primary prevention trial

By: Bill Shrapnel

Bill Shrapnel — Thu, 16 May 2013 00:41:49 +0000

Hi Will
Regarding trans fats, I think the least we can ask of those assessing these studies is that they be consistent. On the one hand, Ramsden et al argue that the Finnish study (which showed the greatest benefit of replacing saturated fat with polyunsaturated fat) was confounded by trans fats and therefore should be excluded from their meta-analysis. But on the other hand they know the Sydney study was confounded by trans fats but include it in their meta-analysis nevertheless. Just inconsistent.
The case that the replacement of saturated fat with linoleic acid alone is detrimental rests on three studies – the Sydney study (discussed above), the Rose study and the Minnesota study. The Rose study was tiny, just 28 people in the corn oil group, very wide confidence intervals, etc.
Which leaves the Minnesota study. Everyone knows why this trial failed – it fell apart. Subjects were supposed to follow the intervention diet for five years but the average time was just one year. No lipid lowering trial with diet would be expected to demonstrate a significant benefit after 12 months. Even treatment with Simvastatin took to longer than this to show benefit in the 4S Study. In the Minnesota study, in those who were on the intervention the longest there was a signal of benefit, not harm, yet Ramsden et al fail to mention this point.
Notwithstanding all of the above, Ramsden et al’s meta-analysis actually shows that replacing saturated fat with mixed polyunsaturated fats (linoleic acid, ALA and long-chain omega 3s) lowers coronary risk. This is what the Heart Foundation of Australia and the National Health & Medical Research Council encourages, as does the American Heart Association I believe. So if everyone agrees on this, let’s support it and implement it. Regards, Bill.

By: Holly

Holly — Mon, 13 May 2013 04:22:01 +0000

Great, I’m looking forward to reading your post on this topic Bill. Coconut oil is becoming really popular amongst the health food community and I often wonder about how healthy it actually is given its saturated fat content.

By: Will

Will — Thu, 09 May 2013 08:53:32 +0000

Hi Bill,

In the original meta-analysis of RCTs by Ramsden and colleagues, the authors had similar TFA-related criticism of the studies included in the Harvard meta-analysis. Wondering if you had any thoughts on this?

http://www.ncbi.nlm.nih.gov/pubmed/21118617
“Both the AHA Advisory(1) and the Mozaffarian et al.(7)
meta-analysis of RCT imprecisely contend that they evaluated the effects of replacing SFA with PUFA, despite the inclusion of the ODHS and other RCT where experimental diets displaced large quantities of TFA-rich partially hydrogenated oils. Indeed, experimental diets replaced common ‘hard’ margarines, industrial shortenings and other sources of TFA in all seven of the RCT included in the meta-analysis by Mozaffarian et al.(7).”

Ramsden, et al tried to account for TFA as well as omega-3 intake in their meta-analysis, which according to my understanding no other meta-analysis has done.

But I agree with your point that we should also consider non-RCT evidence, which on the whole seems to favor polys.

By: Bill Shrapnel

Bill Shrapnel — Wed, 08 May 2013 22:26:05 +0000

Hi Joe
This is very topical – several people have come to me off-line with similar questions, especially in relation to coconut oil. Rather than commenting briefly now, I might take this one on notice and prepare a separate post on it. Watch this space. Regards, Bill

By: Bill Shrapnel

Bill Shrapnel — Wed, 08 May 2013 22:22:38 +0000

Hi Anne.
I (and many others) have concerns about the interpretation of this 40-year old Australian study. The intervention is said to be the replacement of saturated fat with polyunsaturated fat, and the outcome was adverse. However, use of Miracle margarine was central to the intervention. In circa 1970 Miracle margarine contained about 15% of fatty acids as trans fats, so the intervention was actually replacing saturated fats with polyunsaturated fats and trans fats. Trans fats have a strong adverse effect on the risk for coronary heart disease and it is highly likely that the adverse effect observed with this intervention was due to trans fats, not polyunsaturated fats. If the original researchers had had there wits about them they might have identified trans fats as a problem in 1970 rather than leave it to others 20 years later.

However, rather than making decisions on the basis of a single trial, I suggest we look at all the good trials together. Have a look at the meta-analysis I quoted in my blog, conducted by Harvard. It shows that replacing saturated fat with polys lowers coronary risk.

Also, we have to consider other lines of evidence. The evidence from prospective studies shows polys are beneficial with respect to saturated fat. The same goes for the studies into effects on blood lipids. And long-term feeding studies in primates show the same. This is rare consistency in various lines of evidence.

I’ve always thought the data for polys was stronger than for monos – just no primary prevention trials with monos – but the recent trial has help to boost monos claims. Regards, Bill

By: Joe

Joe — Wed, 08 May 2013 08:30:52 +0000

Hi Bill nice summary.
What’s your opinion on saturated fats and whether different sources will affect health outcomes differently? For example saturated fat in butter vs a sausage vs palm oil vs coconut oil.

By: Anne

Anne — Wed, 08 May 2013 02:23:38 +0000

Bill, you say that the weight of evidence still favours polys. I should be interested in you comments on this study: Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of
recovered data from the Sydney Diet Heart Study and updated meta-analysis
BMJ 2013;346:e8707 doi: 10.1136/bmj.e8707

By: Bill Shrapnel

Bill Shrapnel — Tue, 07 May 2013 00:22:21 +0000

Hi Paul. The weight of evidence still favours polys but when you look at macronutrients and CHD risk they now fall into two groups – saturates and carbohydrates in one group and polys and monos in the other, with the latter group being protective relative to the former. I guess I should have said ‘for practical purposes’ there is little to be gained from choosing polys over monos. The thing for nutritionists to get their head around is the equivalence of saturated fat and carbohydrate. Regards, Bill.

By: Paul Jones

Paul Jones — Mon, 06 May 2013 23:53:18 +0000

Agree totally on the need to put forward positive messages on using mono/poly fats in the diet. In practice, I have significantly changed the cardiac recovery talks I do here to reflect this.

Just on one quote from your blog,
“Based on these findings it would appear that there is little to be gained from choosing polys over monos or vice versa – both appear to be good substitutes for saturated fat (and carbohydrate for that matter). Let’s confine the monos versus polys argument to history.”

On the website (http://www.epccs.eu/home/mediterranean-diet-diminishes-cardiovascular-risk), there is a second graph which shows all cause mortality. On this graph, the EVOO diet shows a lower risk, (hazard ratio of 0.81 compared to control, with the nuts diet at 0.95), but not reaching statistical significance (P=0.11).

While this doesn’t answer a poly vs mono question, in that it doesn’t reach statistical significance, I don’t think we can consign the poly vs mono argument to history. Maybe we still need more trials, or larger trials to see if there is a difference.

By: Bill Shrapnel

Bill Shrapnel — Mon, 06 May 2013 23:51:11 +0000

Yes, they had problems trying to get people in the control group to stick to a low fat diet and had to intensify efforts to increase adherence to it. But did you note that the results with the Mediterranean diets were more impressive after this point of the trial than before? Bill