Tag Archives: cardiovascular health

Low-Fat Versus Low-Carb Diet: DIETFITS Show Both Can Work If They Are “Healthy”

In the ongoing nutritional war between adherents of low-fat and low-carb diets, the skeptical cardiologist has generally weighed in on the side of lower carbs for weight loss and cardiovascular health.

I’ve questioned the vilification of saturated fat and emphasized the dangers of added sugar. I’ve even dabbled in nutritional ketosis.

The science in  nutrition is gradually advancing and the DIETFITS study recently published in JAMA is a welcome addition.

DIETFITS is a  really well done study which provides important insights into three huge questions about optimal diet:

  1. Should we choose a low-fat or a  low-carb diet for  weight loss and cardiovascular health?
  2. Do baseline insulin dynamics predict who will respond to low-fat versus low-carb diet?
  3. Can we predict who will respond to low-fat versus low-carb by genetic testing?

The Details Of DIETFITS

Stanford investigators recruited 609 San Francisco area individuals between the ages of 18 to 50 years with BMI of 28 to 40  and randomized them to a “healthy” low-fat diet or a “healthy” low-carb diet.

During the first 8 weeks of the study, low-fat participants were instructed to reduce fat consumption to <20 gm/ day while the low carb participants were instructed to reduce digestible carbohydrate to <20 gms/day.

Then individuals were allowed to add back fats or carbs back to their diets in increments of 5 to 15 g/d per week until “they reached the lowest level of intake they believed could be maintained indefinitely.”  Importantly no explicit instructions for energy restriction were given.

The “healthy” instructions for both groups were as follows

  1. maximize vegetable intake
  2. minimize intake of added sugar, refined flours and trans-fats
  3. focus on whole foods that are minimally processed, nutrient dense and prepared at home whenever possible

Dietfits Outcomes-Diet And Weight

Major findings

  1. Total energy intake was reduced by 500-600 kcal/d for both groups
  2. The low-fat vs the low-carb intake at 12 months was 48% versus 30% for carbs, 29 vs 43% for fat and 21 vs 23% for protein.
  3. Mean 12 months weight change was -5.3 kg for low-fat vs 6-6.0 kg for low-carb which was not significantly different
  4. There was no difference between groups in body fat percentage or waist circumference
  5. Both diets improved lipid profiles and lowered blood pressure, insulin and glucose levels
  6. LDL (bad cholesterol) declined more in the low-fat group whereas HDL (good cholesterol) increased more and triglycerides declined more in the low-carb group.

Thus both diets were successful for weight loss and both improved risk markers for cardiovascular disease after a year.

DIETFITS- Can Genes and Insulin resistance Predict Best Diet?

Surprisingly, the study found no significant diet-genotype interaction and no diet-insulin secretion interaction with weight loss.

This means that they could not predict (as many believed based on earlier studies) who will benefit from a low carb diet based on either currently available genetic testing or a generally accepted measure of insulin resistance.

As the authors point out, these findings “highlight the importance of conducting large, appropriately powered trials such as DIETFITS for validating early exploratory analyses.”

DIETFITS-Perspectives

As you can imagine this study has led to quite an uproar and backlash from dedicated combatants in the macronutrient wars.

A reasoned summary and response from Andreas Eenfeldt, a low carb proponent can be found on his excellent low carb/keto Diet Doctor site here.

Eenfeldt concludes

If I’m allowed to speculate, the reason that we did not see any major additional benefit from low carb in this study is that the groups ended up so similar when it came to bad carbs. The low-fat group ended up eating fewer carbs too (!) and significantly less sugar, while the low-carb group ended with a somewhat weak low-carb diet, reporting 130 grams of carbs per day.

Eenfeldt emphasizes that low-fat diets never “win” these macronutrient dietary skirmishes:

On the whole, this study adds to the 57 earlier studies (RCTs) comparing low carb and low fat for weight loss.

From a standing of 29 wins for low carb, zero for low fat and 28 draws, we now have 29 wins for low carb and 29 draws. The wins for low fat stay at zero.

Larry Husten at Cardiobrief.org in his analysis of the study quotes a number of experts including Gary Taubes, the low carb pioneering journalist

Taubes speculates “that the weight loss may have been similar not because any diet works if you stick with it and cut calories (one possible interpretation) but because of what these diets had in common — avoid sugar, refined grains, processed foods. Whether the low-carb arm would have done even better had Gardner kept their carbohydrates low is something this study can’t say. (And Ornish [low-fat diet proponent] would probably say the same thing about fat consumption.)”

The low-fat or vegan disciples seem to have had a muted response to this study. I can’t find anything from John McDougal , Dean Ornish, Caldwell Esselstyn or Joel Fuhrman.

Readers feel free to leave comments which  link to relevant analysis from the low-fat proponents.

Dietfits-Perspective Of The Participants

Julia Volluz at Vox wrote a fascinating piece recently which involved interviewing some of the participants in this study.

She points out that although the average DIETFITS participant lost over 10 pounds, “Some people lost more than 60 pounds, and others gained more than 20 during the year.”

LOW_FAT_LOW_CARBS_DIETS1__1_

She obtained permission from the lead author, Christopher Gardner  and interviewed  “Dawn, Denis, Elizabeth*, and Todd — two low-fat dieters and two low-carb dieters — about their experiences of succeeding or faltering in trying to slim down”

LOW_FAT_LOW_CARBS_DIETS1

I highly recommend reading the entire article for details but Volluz concludes

And that leads us to one of the burning mysteries of diets: how to explain why some people fail where others succeed — or the extreme variation in responses. Right now, science doesn’t have compelling answers, but the unifying theme from the four study participants should be instructive: The particulars of their diets — how many carbs or how much fat they were eating — were almost afterthoughts. Instead, it was their jobs, life circumstances, and where they lived that nudged them toward better health or crashing.

DIETFITS-Importance of “Healthy” Diet

Most likely the success of both of these diets is due to the instruction that both groups received on following a “healthy” diet. This guidance is remarkably similar to what I advocate and is something that combatants in the diet wars ranging from paleo to vegan can agree on.

The JAMA paper only provides the description I listed above but Volluz adds that participants were instructed to:

… focus on whole, real foods that were mostly prepared at home when possible, and specifically included as many vegetables as possible, every day … choose lean grass-fed and pasture-raised animal foods as well as sustainable fish ... eliminate, as much as possible, processed food products, including those with added sugars, refined white flour products, or trans-fats … prepare as much of their own food as possible. …

Indeed, if you want to see a very detailed description of the instructional process for participants check out the very detailed description of the methods here.

Yours in Health,

-ACP

N.B. I was searching for a reasoned response to this study from the low fat camp and to my surprise came across this fascinating video featuring the lead author of the study, Christopher Gardner, on (no fat/vegan) John McDougal’s YouTube site. Gardner is clearly on the side of sustainable, local , ethical food consumption but to his credit, his research , publications and comments on DIETFITS don’t reveal this.

Beware Of More Misinformation From The American Heart Association On Coconut Oil and Saturated Fats

In a “presidential advisory” to the American Heart Association (AHA)  a panel of experts last week  strongly endorsed the heart healthy benefits of replacing any and all saturated fats in our diet with vegetable oils (like corn , soy, and canola oil) which contain predominantly poly  or mono unsaturated fats.

Examining the metrics of this article it appears that the vast majority of news media reporting on it have lead with a headline that reads:

  Coconut oil isn’t actually good for you, the American Heart Association says     

Given this brazen attempt by the AHA to smear coconut oil’s reputation I felt compelled to revisit my analysis of coconut oil from a year ago. I’ve included new discussion on a key paper referenced by the AHA advisory and some words of wisdom from Gary Taubes.

Coconut Oil: Poster Child for Dietary Fat Confusion

Coconut oil (CO) is a microcosm of the dietary confusion present in the U.S. On one hand a CO Google search yields a plethora of glowing testimonials to diverse benefits: Wellness Mama lists “101 Uses for Coconut Oil,” Authority Nutrition lists “10 Proven Health Benefits.”

On the other hand, the  American Heart Association (AHA) and the USDA’s Dietary Guidelines For Americans warn us to avoid consuming coconut oil  because it contains about 90% saturated fat (SFA) which is a higher percentage than butter (about 64% saturated fat), beef fat (40%), or even lard (also 40%)

In many respects, the vilification of coconut oil by federal dietary guidelines and the AHA resembles the inappropriate attack on dairy fat and is emblematic of the whole misguided war on dietary fat. In fact, the new AHA advisory  after singling out coconut oil goes on to cherry-pick the data on dairy fat and cardiovascular disease in order to  support their faulty recommendations for choosing low or nonfat dairy..

The AHAs simple message to replace all saturated fats in your diet with poly unsaturated fats (PUFAs) or monounsaturated fats (MUFAs) is flawed because:

  1. All saturated fats are not created equal :the kinds of saturated fats in coconut oil differs markedly from both dairy SFAs and beef SFAs . Some  SFAs may have beneficial effects on blood lipids, weight, and cardiovascular health.

  2. The types of nonSFAs in vegetable oils differ markedly and may have differential effects on cardiovascular health.

All Saturated Fats Are Not Created Equal!

Saturated fats are divided into various types based on the number of carbon atoms in the molecule. Depending on length, they differ markedly in their metabolism, absorption and effects on lipid profiles.

The major SFA in coconut oil, lauric acid, has a 12 carbon chain and is thus considered a medium chain fatty acid (MCFA).

The AHA advisory makes a cursory attempt to address the huge hole in their logic primarily relying on a meta-regression analysis published in 2003 by Mensink, et al., and concludes:

The Mensink meta-regression analysis determined the effects on blood lipids of replacing carbohydrates with the individual saturated fatty acids that are in common foods, including lauric, myristic, palmitic, and stearic ac- ids. Lauric, myristic, and palmitic acids all had similar effects in increasing LDL cholesterol and HDL cholesterol and decreasing triglycerides when replacing carbohydrates

In summary, the common individual saturated fats raise LDL cholesterol. Their replacement with monounsaturated or polyunsaturated fats lowers LDL cholesterol. Differences in the effects of the individual fatty acids are small and should not affect dietary recommendations to lower saturated fat intake.

But if we examine what the actual paper by Mensink et al (available in full here) we find their conclusions are the exact opposite of the AHA:

Lauric acid greatly increased total cholesterol, but much of its effect was on HDL cholesterol. Consequently, oils rich in lauric acid decreased the ratio of total to HDL cholesterol. Myristic and palmitic acids had little effect on the ratio, and stearic acid reduced the ratio slightly.

The differences in the effects of the individual fatty acids are not small they are quite significant if we look at the totality of the effects on lipids relevant to cardiovascular disease. In their discussion, Mensink, et al go on to say:

Our results emphasize the risk of relying on cholesterol alone as a marker of CAD risk. Replacement of carbohydrates with tropical oils markedly raises total cholesterol, which is unfavorable, but the picture changes if effects on HDL and apo B are taken into account.

What’s more :

The picture may change again once we know how to interpret the effects of diet on postprandial lipemia, thrombogenic factors, and other, newer markers. However, as long as information directly linking the consumption of certain fats and oils with CAD is lacking, we can never be sure what such fats and oils do to CAD risk.

This graph from Mensink, et al. shows what would happen to the total/HDL cholesterol ratio if we substituted various foods in place of 10% mixed fat. Theoretically a lower ratio is more heart healthy. Look at the drastic differences between palm oil, coconut oil and butter, all of which are condemned by the AHA

 

Misguided Dietary Fat Recommendations

The  AHA experts have doubled down on their recommendation to use cooking oils that have less saturated fat such as canola and corn oil. They advise, in general, to “choose oils with less than 4 grams of saturated fat per tablespoon.”

Screen Shot 2016-05-07 at 12.28.40 PMCanola and corn oil, the products of extensive factory processing techniques, contain mostly mono or polyunsaturated fats which have been deemed “heart-healthy” on the flimsiest of evidence.

The most recent data we have on replacing saturated fat in the diet with polyunsaturated fat comes from the Minnesota Coronary Experiment performed from 1968 to 1973, but published in 2016 in the BMJ.

Data from this study, which substituted liquid corn oil in place of the usual hospital cooking fats, and corn oil margarine in place of butter and added corn oil to numerous food items, showed no overall benefit in reducing mortality. In fact, individuals over age 65 were more likely to die from cardiovascular disease if they got the corn oil diet.

Cherry-Picking Data

The new AHA presidential advisory doesn’t include this study or  data from the Sydney Heart Study, another study with negative results for substituting PUFAs for SFAs.

As Gary Taubes pointed out in a post for Larry Husten’s cardiobrief.org blog, the AHA experts cherry-picked four “core trials” that  agreed with their hypothesis and excluded the ones that don’t agree:

They do this for every trial but the four, including among the rejections the largest trials ever done: the Minnesota Coronary Survey, the Sydney Heart Study, and, most notably, the Women’s Health Initiative, which was the single largest and most expensive clinical trial ever done. All of these resulted in evidence that refuted the hypothesis. All are rejected from the analysis. And the AHA experts have good reasons for all of these decisions, but when other organizations – most notably the Cochrane Collaboration – did this exercise correctly, deciding on a strict methodology in advance that would determine which studies to use and which not, without knowing the results, these trials were typically included.

Coconut Oil: The Bottom Line

After all is said and done, it would appear that coconut oil, despite coming from a vegetable, resembles dairy fat in many ways.

It is more likely than not that coconut oil, like dairy fat, reduces your chances of obesity and heart disease, especially when compared to the typical American diet of highly processed and high carbohydrate foods.

Although containing lots of saturated fat, the SFAs in coconut oil are drastically different from other dietary sources of SFA.  The medium chain fatty acids like lauric acid which make up the coconut are absorbed and metabolized differently from long chain fatty acids found in animal fat.

The only explanation for dietary guidelines advising against coconut oil and dairy fat is the need to stay “on message” and simplify food choices for consumers, thus continuing the vilification of all saturated fats.

Substituting corn oil (or other vegetable oils with lots of linoleic acid) for foods containing saturated fats does not lower risk of heart disease and may promote atherosclerotic outcomes like heart attack and stroke.

Finally, I agree with Taubes that we deserve good scientific studies proving without a doubt that these drastic changes in diet are truly helping:

“telling people to eat something new to the environment — an unnatural factor, à la virtually any vegetable oil (other than olive oil if your ancestor happen to come from the Mediterranean or mid-East), …..is an entirely different proposition. Now you’re assuming that this unnatural factor is protective, just like we assume a drug can be protective say by lowering our blood pressure or cholesterol. And so the situation is little different than it would be if these AHA authorities were concluding that we should all take statins prophylactically or beta blockers. The point is that no one would ever accept such a proposal for a drug without large-scale clinical trials demonstrating that the benefits far outweigh the risks. So even if the AHA hypothesis is as reasonable and compelling as the AHA authors clearly believe it is, it has to be tested. They are literally saying (not figuratively, literally) that vegetable oils — soy, canola, etc — are as beneficial as statins and so we should all consume them. Maybe so, but before we do (or at least before I do), they have a moral and ethical obligation to rigorously test that hypothesis, just as they would if they were advising us all to take a drug.”

Cocovorically Yours,

-ACP

For those seeking more information.

This graph is from the BMJ paper which also included a meta-analysis of all randomized studies substituting linoleic acid for saturated fat.  The data do not favor substituting corn oil for saturated fat

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