Sunday, July 28, 2013

Why We Should Question Dietary Advice: Summary and Implications

Summary 

Most of the evidence that forms the basis of national dietary guidelines and position statements of health authorities comes from observational studies where they find correlations between diet and disease.  While you shouldn’t draw conclusions from observational studies anyway, observational studies of this type are notoriously unreliable because of the large number of confounding variables and inaccurate self-reporting.  Just because something has a positive relationship in observational studies doesn’t mean it will hold up in clinical trials as evidenced by hormone replacement therapy, grain fibre, etc. 

Many health authorities have financial ties to the food industry.  While they say that the need to work with industry, the reality is that the food industry funds education programs that spread propaganda to protect their interests.  The financial ties to the food industry are also an implicit endorsement of their products, intentional or not 

Most dietary recommendations include the reduction of saturated fat and trans fats, and often replacing them with polyunsaturated fats, to reduce cholesterol, thereby lowering the risk of cardiovascular disease.  However, replacing saturated fat with linoleic acid (an omega 6 polyunsaturated fat) increases cardiovascular disease and total mortality in controlled clinical trials.  The disaster with artificial trans fats should be a warning against other new additions to the food supply 

One of the most common and unquestioned bits of dietary advice is to reduce salt to lower pressure.  However, reducing salt has a very mild effect on blood pressure and doesn’t reduce mortality, suggesting it is far from being the primary cause of hypertension.  Salt reduction has some adverse effects: it increases the renin-angiotensin-aldosterone system and noradrenaline, and actually increases mortality in a few diseases. 

One would think that a perquisite of good diet advice is that the recommended diet is at least adequate in all nutrients (depending on the criteria for adequacy).  However, most dietary advice suggests reducing (or at least not promoting) choline rich foods such as eggs and liver (due to unfounded dietary cholesterol concerns).  The result is that most people are choline deficient 

The dietary guidelines and other sources of diet information regularly reduce foods or food groups to a few nutrients such as protein, iron and fibre.  They then group foods into groups based on similarities in only a few nutrients such as the dairy and meat alternatives, even though the dairy and meat alternatives have a very different nutrient profile to dairy and meat, even if they are rich in calcium or protein.  This may result in poor, unbalanced nutrient intakes 

The dietary guidelines and other sources diet information often have a biased ranking of nutrient density they mention the benefits of fibre and phytonutrients, but don’t mention the benefits of non-essential nutrients in animal foods such as carnitine, carnosine, creatine, taurine and coenzyme Q10 


Implications 

  • Be sceptical when observational studies are used to claim causality
  • Be especially sceptical of diet epidemiology and advice that relies on it heavily
  • Be sceptical of advice coming from people/groups with conflicts of interest
  • Replacing saturated fats with vegetable oils won’t reduce the risk of cardiovascular disease
  • Don’t eat artificial trans fats (natural trans fats are fine) and be sceptical of new additions to the food supply
  • Low salt diets won’t reduce blood pressure by much and may be harmful
  • Get enough choline (eggs, liver)
  • Don’t be a reductionist, there is more to food than a few nutrients here and there
  • Omnivorous diets are best for meeting our nutrient needs
  • Appreciate the non-essential nutrients and beneficial compounds in both plant and animal foods

Sunday, July 21, 2013

Why We Should Question Dietary Advice: Part 3

Choline

Eggs and organ meats have been demonised in the past due to their high cholesterol content.  Some, but not all, dietary recommendations now don’t recommend against dietary cholesterol and do recommend a small number of eggs.  Eggs and organ meats are two of the few reliable sources of choline in the diet. 

Humans seem to have a large requirement for choline.  The adequate intake (AI) comes largely from this study which found that 500mg of choline was sufficient to prevent an increase in liver enzymes in plasma (which is a of signal liver damage) in healthy adults [1].  So add 10%, use body mass to adjust for women, and you’ve got your AI [2].  Seeing as 500mg was simply sufficient to prevent liver damage it’s debatable whether 550/425mg is enough for good health. 

Regardless of whether we should be eating more than 550/425mg of choline daily or not, it doesn’t change how hopelessly deficient in choline current dietary recommendations are.  The Mediterranean diet and the DASH diet, which are very similar to what the dietary guidelines recommend, only provide 55% and 46% of the choline requirement for men* [3].  To meet the requirement these diets would need to include an average of 2 eggs or 50-100g of liver daily.  As expected, in the real world most people are choline deficient [4] [5]

* Sometimes in the USDA database choline and other nutrients aren’t measured.  This study did also use World’s Healthiest Foods database, but even so the choline numbers will probably be slightly higher 

Severe Reductionism and Inappropriate Classification

The dietary guidelines (and poorer quality sources of dietary advice in particular) have a habit on reducing entire food groups to a few nutrients.  Little attention is given to the nutrients not on this list 

The Sum of Nutrients In Dietary Advice
Good Nutrients:
  • Protein 
  • Complex Carbohydrates
  • Fibre 
  • Calcium 
  • Iron
  • Zinc 
  • ‘Antioxidants/Phytochemicals’
Bad Nutrients:
  • Fat (sometimes) 
  • Saturated Fat 
  • Sugar (sometimes)
  • Salt

I think to a large extent they are fighting the wrong battles.  But anyway, what this also means it that if you reduce a food group to one or a few nutrients then anything with those nutrients is considered an ‘alternative’ regardless of the often large differences in the rest of the nutrient profile.  For example the dietary guidelines reduces dairy foods to calcium so anything high in calcium, like calcium fortified, soy imitations of dairy foods are considered a dairy alternative (see Dairy and Alternatives) and they reduce meat to protein so anything high in protein like legumes are considered a meat alternative (see Meat, Eggs and Alternatives)*.  This is despite dairy and meat being far better sources of their ‘key’ nutrient (bioavailability, etc) and having a very different nutrient profile to their plant-based ‘alternatives’ 

* The 2011 draft for the Australian dietary guidelines described nuts and seeds as being protein rich even though almost all nuts and seeds contain less than 15% of their total calories as protein. 

** Another form of reductionism is the frequent grouping and classification of SFA and artificial TFA as ‘bad fats’ simply because they both increase LDL-C 

‘Nutrient Density’

Dr Joel Fuhrman developed the ANDI system for nutrient density which excludes some essential nutrients (some vitamins and minerals, DHA, etc) and includes some non-essential nutrients (like phytochemicals).  The net result is that under this ranking system fruits and vegetables perform well and animal foods perform badly [6]. 

The Australian dietary guidelines (no doubt others) do the same thing although to a lesser extent.  They don’t define nutrient density and they don’t deliberately ignore certain micronutrients, but what they do is reduce food groups to a few nutrients and discuss non-essential nutrients found in plants such as fibre and phytochemicals but not the non-essential nutrients found in animal foods such as carnitine, carnosine, creatine, taurine and coenzyme Q10*.  Check the links for research related to them.  I’m far more excited about the potential of them in clinical trials than I am with fibre and phytochemicals. 

See the table in Meat, Eggs and Alternatives for a general sense or which nutrients plant and animal foods tend to be rich in.  From our perspective as omnivores the even distribution should hardly be surprising.

* Some plant foods are good sources of CoQ10 too [7] 

** I recently listened to this debate between Dr Eric Westman and Dr T Colin Campbell.  At one point Colin Campbell said meat has no antioxidants.  It’s sad really, for all his titles and letters, he isn’t even aware of carnitine, carnosine, creatine, taurine or CoQ10 (probably others too). 

Further Reading:
(1) Meeting the Choline Requirement -- Eggs, Organs, and the Wheat Paradox

Sunday, July 14, 2013

Why We Should Question Dietary Advice: Part 2

Saturated Fat and Trans Fat 

Due to diet heart hypothesis (saturated fat >> cholesterol >> CVD), the first dietary guidelines for Americans recommended replacing animal fats and tropical oils with vegetable oils and margarine, regardless of the trans fat content of the vegetables oils and margarine.  And in the 1980’s the CSPI lobbied fast food to replace animal fats with partially hydrogenated vegetable oils.  There are two problems with this: 

1.      Saturated fat doesn’t increase CVD
2.      The artificial trans fats are toxic 

Concerns about artificial trans fats were raised in the 1970s by Mary Enig who was ignored and silenced for decades.  Artificial TFA only started to be taken seriously in the 90’s perhaps because in 1992 Walter Willett found an association between trans fats and CVD in the Nurse’s Health Study [1].  After more research in the 90’s, the FDA decided to have TFA on labels in 1999 [2].  (In the US food products can have up to 0.5g of TFA per serve.  Food manufactures can get around this by decreasing serving size and by having artificial TFA in mono- and diglycerides). 

We may have largely sorted out the artificial TFA problem now (not quite as it's still in the food supply), but before we get smug, I don’t think history will be kind on us either

Artificial TFA were introduced to the food supply in the 1910’s, decades past until their effects were researched and then two more decades past until those concerns were taken seriously and no longer ignored and silenced (although artificial TFA are still in the food supply).  True, regulations may be tighter now and we do have the internet, but I suspect history will repeat itself many times: 

  • Food manufactures create product
  • Industry promotes their product to health authorities using industry funded studies
  • Health authorities endorse product based on the results of biased studies and financial ties to industry
  • Sometime later, independent studies find the product is harmful 
  • More time passes until the independent studies are taken seriously rather than being inappropriately ignored, criticised or silenced, or perhaps this never happens 

Remember, half the reason for using artificial TFA was that replacing animal fats with vegetable oils, specifically SFA with linoleic acid, was supposed to reduce CVD.  Instead swapping SFA for linoleic acid seems to increase LDL oxidation and CVD.  To avoid writing the same stuff again see , The Diet Heart Hypothesis (most important) and Fats and LDL Oxidation.  Also see DGA2011 - Total Fat and Saturated Fat for

Health experts and the media often group artificial TFA (elaidic acid) and natural TFA (vaccenic acid and CLA) together as if they’re the same thing.  Elaidic acid has many negative effects beyond increasing the TC:HDL-C ratio, whereas natural TFA doesn’t share those negative effects and has some positive effects.  This shouldn’t be too surprising as natural TFA have probably been part of our diet for 2 million years and is also found in breast milk.  Breast milk also contains SFA, apparently your mother was trying to kill you

Also, on a somewhat related note, most dietary advice suggests reducing fat for weight loss and CVD, which is the reason why low-fat dairy and lean meat is specifically recommended.  Never mind that high fat dairy is either inversely associated with, or not related to obesity and CVD [3] (if you're going to use diet epidemiology to make recommendations, you could at least be consistent).    Anyway, low carb diets just as, if not more effective (at 6 months) than low fat diets for weight loss, and also improve cardiovascular risk factors like the Total:HDL-C ratio and triglycerides better than low fat diets.

See DGA 2011 - Total Fat and Saturated Fat: Part 1 and 2

Salt 

Reducing salt is a fairly universal dietary recommendation that has its basis in the assumption that high sodium intakes cause hypertension.  A Cochrane review found that while sodium intake has an effect on blood pressure, the effect is small and is therefore unlikely that high sodium intakes are the cause of hypertension. 

[3]
Systolic
Diastolic
Mainly Caucasians – High Blood Pressure
-4.18
-1.98
Mainly Caucasians – Normal Blood Pressure
-1.27
-0.54
African Americans – Normal and High Blood Pressure
-6.44
-1.98

However, salt restriction increases the activity of the renin-angiotensin-aldosterone system (the RAAS)* by more than 300%, increases noradrenaline by 30% and adrenaline by 12% [3].  Salt restriction can lead to an increase in insulin resistance through noradrenaline [4] and an increase in oxidative stress though the RAAS [5] 

Most importantly a Cochrane review found that salt restriction didn’t reduce all-cause mortality (there was a non-significant reduction in mortality) [6].  Some studies find salt restriction may increase all-cause mortality in some diseases such as T1D [7], heart failure [6] and hypertension [8] and may increase the risk of developing end-stage renal disease [7].  It's very interesting that the diseases blamed on salt and/or hypertension, heart failure, hypertension and end-stage renal disease, are the ones where reducing salt may be harmful, which is probably due to up regulation of the RAAS (the therapeutic target of some anti-hypertensives).  We shouldn’t generalise from disease states to other contexts

Further Reading:
(1) The Oiling of America
(2) Stop Trans Fat
(3) Salt and Blood Pressure
(4) Sodium Intake in Populations: Assessment of Evidence

Sunday, July 7, 2013

Why We Should Question Dietary Advice: Part 1

So diet and health are important, does that mean you should read your country’s dietary guidelines and blindly follow them?  I don’t think so.  I raised some objections to the draft for the new Australian Dietary Guidelines that I wrote a while ago (see here).  If I had to write it again I would add some things (like salt) and make a few changes.  The actual guidelines were released in April this year (see here).  Besides the submission, in this three part series I’ll give some reasons why we should question the standard dietary advice.

Recommendations from Observational Studies 

I haven’t read the USDA dietary guidelines, but I have read the Australian ones and I suspect they are very similar.  The Australian dietary guidelines mostly use observational studies to justify their recommendations, but there are some problems with this. 

The major weakness of many observational studies are confounding variables, particularly where humans are involved.  In diet related observational studies there are stacks of confounding variables.  To make things simple let divide the population into ‘health conscious’ and ‘not health conscious’.  The table below compares some of the differences. 

Health Conscious
Not Health Conscious
Diet
More fruits, vegetables, whole grains, legumes, nuts, fish and reduced fat dairy.  Low fat, SFA, TFA, salt and sugar
More junk food, meat, eggs, full fat dairy, refined grains.  High fat, SFA, TFA, salt and sugar
Lifestyle
More exercise, more and better sleep, better educated, higher income, more health check-ups
More smoking, heavy drinking, less education, lower income, fewer health check-ups

I could keep going on, but these are the most obvious differences.  The point is that if you do yet another ‘meat causes cancer’ observational study, the problem (besides the clichĂ© correlation doesn’t equal causation) is that there are many confounding variables.  How can you be sure that you are measuring the relationship between just meat and cancer.  Even if you adjust for all the other factors on the list, you can’t adjust for the factors you don’t measure.

There have been occasions where something that looks good in observational studies actually performs badly in RCTs, such as hormone replacement therapy (HRT) (in the WHI [1]) and grain fibre (in DART [2]).  This is because people were told that HRT and grain fibre were good for them, so then the health conscious people get HRT and eat grain fibre.  As a result they look favourable in observational studies even through they have been found to be harmful in RCTs, because they positive effect of all the confounding variables they didn't adjust for in the observational studies were greater than the negative effect of HRT, grain fibre, etc.  This is called the healthy user effect or healthy adherer effect and has been seen elsewhere, such as: vitamin supplementation, statins for other diseases and flu vaccines [3]

In my submission to the draft dietary guidelines last year I disagreed with the DAA when they said 

“Not a lot has changed in the new draft Guidelines, which shows we’ve generally been on the right track with the food and nutrition advice we’ve been giving Australians.” 

All this shows is that: 

  • You recommend X
  • Health conscious people eat X
  • Future observational studies show X is associated with better health
  • You therefore conclude X is good and you recommend X
 
There are other issues in observational studies [4]:
 
  • Food frequency questionnaires (FFQs) are used to assess food intake.  But FFQs are done very infrequently (generally less than once a year) and require people to accurately estimate their food consumption from years ago, even though they can't accurately report what they ate 24 hours ago
  • People underreport calories and 'bad' foods, while over-reporting 'good' foods and exercise.  This is particularly true with face-to-face interviews and people who are overweight do this even more (called 'self-report bias')

Researchers who conduct observational studies are also guilty of making recommendations based on observational studies.  A recent study found that in 56% of the observational studies examined, the authors made a clinical recommendation, whereas only 14% of the authors mentioned a need for RCTs [5] 

* Another weakness of observational studies, some more so than others, is confusing the most likely cause an effect.  For example, let’s say you do a study and find that a higher proportion of people with depression are taking antidepressants and then conclude that antidepressants cause depression.  This can be an issue in some medical related studies, but usually not much of an issue in diet studies, maybe except for stuff like calcium/dairy intake and osteoporosis 

** I like using observational studies where confounding variables are less likely to be a factor.  For example, ones that compare a genetic polymorphism with a disease to provide supporting evidence for a particular mechanism.  Such as the GG genotype for MPO, which results in a higher expression of MPO and has an HR of 5.5 for CV events (also note the high HR as opposed to the ~1.1 that you often see in ‘meat causes cancer’ studies).  See Immune Related Mechanisms (of Atherosclerosis) 

Ties to the Food Industry 

The organisations giving out dietary advice may receive corporate sponsorship from the food industry.  An example of this is the AND, which receives sponsorship from big businesses who produce junk/processed food, such as The Cocacola Company, Kelloggs, Mars Food, ConAgra and General Mills, as well as others such as the National Cattleman’s Beef Association and the National Dairy Council.  It wouldn’t be a big deal if the AND just said ‘thanks for money, goodbye', but as you probably suspect that’s not what’s happening.  What is happening is this: 

  • “Companies on AND’s list of approved continuing education providers include Coca-Cola, Kraft Foods, NestlĂ©, and PepsiCo.”
  • “Among the messages taught in Coca-Cola-sponsored continuing education courses are: sugar is not harmful to children; aspartame is completely safe, including for children over one year; and the Institute of Medicine is too restrictive in its school nutrition standards.” 
  • “At AND’s 2012 annual meeting, 18 organizations – less than five percent of all exhibitors – captured 25 percent of the total exhibitor space. Only two out of the 18 represented whole, non-processed foods.” 
  • “Roughly 23 percent of annual meeting speakers had industry ties, although most of these conflicts were not disclosed in the program session description.”
  • “To date, AND has not supported controversial nutrition policies that might upset corporate sponsors, such as limits on soft drink sizes, soda taxes, or GMO labels” 
  • Also something that is quite telling “That AND saw no conflict of interest in using industry money to study the potential bias of using industry money is troubling to say the least.”
  • “Historically, the Academy has never been much of a leader on nutrition policy and at times, quite the opposite. For example, in 1999, the Academy actually opposed mandated labeling of “trans fats” on food packaging” 

The AND and others will tell us that they need to work with the food industry to reduce obesity/T2D/CVD/etc, but of course that’s rubbish.  The food industry is the problem and they aren’t likely to ever be part of the solution*.  (One could argue that if the AND is in it for its members then: promote junk food as part of a ‘balanced diet’ >> more obesity >> more consults for dieticians) 

Now it would be wrong to use this information to completely ignore what the AND has to say, nor should this be a negative reflection on dieticians (the majority of whom find sponsorship from junk food corporations to be unacceptable), that would be ad hominem.  However, I think it’s appropriate to question the AND’s motivations and to look elsewhere for your primary source of nutrition advice 

See And Now a Word From Our Sponsors (It’s worthwhile to read the whole thing) 

It’s likely this problem exists, perhaps not on the same magnitude, with other organisations and in other countries.  Most Australian’s have seen the Heart Foundation’s tick of approval on junk food like most breakfast cereals and cereal bars, the University of Sydney’s nutrition department* has McDonalds and Kelloggs, among others, as corporate governors [6] and of course there’s the USDA handing out dietary advice. 

* In this article the author discusses ‘how junk food can end obesity’ with a model of obesity that is as reductionist as sugar, salt and fat.  So we blame junk food for being too high in sugar, salt or fat, then the manufactures change a few things, but how well has sugar alcohols/aspartame, MSG and olestra/guar gum/xanthin gum worked for us.  Or instead we blame junk food for being low in nutrients, then the manufactures add a few things, but free iron is great for bacterial overgrowth, folic acid promotes cancer growth and multivitamins may increase mortality. 

** You may remember the University of Sydney’s nutrition department for 'The Carnivore Connection Hypothesis' (see my take here and here) and 'The Australian Paradox' (that apparently Australian’s are eating less sugar now than they did a few decades ago.  See this website) 

Further Reading:
(1) Healthy User and Related Biases in Observational Studies of Preventive Interventions: A Primer for Physicians
(2) Modern Diet-Health Epidemiology: a Self-Fulfilling Prophecy? Part I
(3) Modern Diet-Health Epidemiology: a Self-Fulfilling Prophecy? Part II
(4) The Challenges and Failures of Nutrition Studies
(5) And Now a Word From Out Sponsors
(6) Heart Foundation says sugar isn't relevant