Friday, August 22, 2014

Is it time to rethink nutrition's public enemies 1 and 2, saturated fat and salt? (Part 1)

Few nutrients are viewed in a more negative light than salt and saturated fat. The infamous "Seven Country Study" by Ancel Keys from the 1950's brought about a crusade to rid the American diet of fat. Since, more is now known about the differing physiological effects of different types of fatty acids (saturated, trans, monounsaturated, and polyunsaturated). Though some fat sources are now generally considered "healthy," like those associated with a "Mediterranean Diet" such as olive oil, nuts, and fish, conventional guidance still puts saturated fat in the "less is better" category. We often continue to hear how it's best to substitute saturated fat with polyunsaturated fats (see a previous blog I did on this topic) Similarly, salt (actually sodium, which is one mineral found in naturally occurring salt) receives a pretty bad rap because of its link with blood pressure. With greater numbers of people experiencing hypertension (high blood pressure), sodium became the primary target. Cut the sodium, reduce the high blood pressure. (If you haven't, take a look at the recently published book by Michael Moss, Salt Sugar Fat: How the Food Giants Hooked Us, which argues fat and salt form two parts of nutrition's current three-headed monster.) 

The current "Dietary Guidelines for Americans," which the U.S. Government updates and releases every five years puts both saturated fat and sodium in the "foods and foods components to reduce" category. It states, 

  • "Reduce daily sodium intake to less than 2,300 milligrams (mg) and further reduce intake to 1,500 mg among persons who are 51 and older and those any age who are African American or have hypertension, diabetes, or chronic kidney disease. The 1,500 mg recommendation applies to about half of the U.S. population, including children, and the majority of adults.

  • Consume less than 10 percent of calories from saturated fatty acids by replacing them with monounsaturated and polyunsaturated fatty acids."

Other nutrition guidelines are slightly more stringent in some respects. The American Heart Association advises to:

  • "…reduce saturated fat to no more than 5 to 6 percent of total calories. (Just to put this into perspective, if a person is eating 2,000 calories a day, this amounts to a little more than 1 tablespoon of butter per day or 2 large fried eggs.)

  • Choose and prepare foods with little or no salt…aim to eat no more than 2,400 milligrams of sodium per day. Reducing daily intake to 1,500 mg is desirable because it can lower blood pressure even further."

However, research is continuing to show that nutritional guidance related to both saturated fat and sodium may require a more nuanced approach (as many things in nutrition often do). Before going even further, though, I want to point out the delicate balance that must be struck between public health guidance (like those cited above) and individual nutrition and health outcomes. This is particularly challenging in nutrition. No two individuals are exactly alike and thus have slightly different biologies. As a result, my physiological response to say a high-carbohydrate meal might be slightly different than yours. Genetics plays a role in this. For example, fascinating research presented by Chris Masterjohn at the 2012 Ancestral Health Symposium on salivary amylase (one of the first enzymes your body uses to digest starches/carbohydrates in the mouth) has shown that the ability to digest starches varies from population to population. In other words, some populations, such as those in east Asia, whose diets contain a fair amount of carbohydrate (think white rice), have evolved to produce more amylase then say the Inuits. These important distinctions across populations means general guidelines may not be applicable (or worse, even harmful) for all.

The basic message: public health guidance tends to be extremely broad, focused on what's generally best for groups of people. Metabolism, however, is extremely individualized, often requiring a more nuanced approached. 

Okay, back to fat and sodium.

Some interesting new research published in the past few weeks provides more evidence for why current mainstream guidance may need to be adjusted (coincidentally, the next version of the Dietary Guidelines for Americans are being discussed and are set to be released in 2015). 


One of the biggest challenges with current guidance on fat is it often overlooks complexity. As I've said before, not all fats are the same (just as not all calories are equal, see this previous post), each having different metabolic and health effects. Because of this, I think it's much more useful to think of food as "information" rather then exclusively "energy." As I've written before, 100 calories of soda tells the body to react in a very different way (think insulin release) then 100 calories of butter. Foods are also not all exclusively "saturated fat" or "unsaturated fat," but rather a mixture. The predominant type of fat usually is the one used to categorize a food as saturated, poly-unsaturated, mono-unsaturated, etc. 

Saturated fat has been public enemy number one, particularly with heart disease on the rise in the United States and globally. But, more research is showing this might be misguided. A 2010 meta-analysis (which included one of the foremost experts on heart disease and cholesterol, Ronald Krauss as an author) found "no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD [coronary heart disease] or CVD [cardiovascular disease]." 

A recent study published in The Lancet attempts to shed some light as to why we hear these conflicting messages: sometimes saturated fat is okay, other times it's not (see the evolution of Time Magazine covers below as an example). One explanation is that it has to do with the length of the carbon chain comprising the fatty acid "tail." (Warning: biochemistry ahead). As there are different types of fats (unsaturated has one or more double bonds connecting two carbon atoms, while saturated fats don't have any), fatty acids can also have varying lengths of fatty acid chains. Short-chain fatty acids, such as butyric acid, have fewer than 6 carbons, while long-chain fatty acids can have 22 carbons or more.

Cholesterol Cover Time Magazine
The study used a sub-set of 16,154 people from eight European countries from the EPIC-Interact study to investigate the association between saturated fatty acids and type 2 diabetes. Researchers used a pretty sophisticated procedure of converting the fatty acids into a more volatile state and separating them using gas chromatography. They looked at 37 different fatty acids. 

What did they find? Even-chain fatty acids had the greatest contribution to type 2 diabetes risk. "Older adults, those with higher BMI, and men had higher relative concentrations of even-chain SFAs, whereas we noted the opposite for longer-chain SFAs. Relative concentrations of odd-chain SFAs were higher in people with a lower BMI and in women."
Researchers also conducted an analysis of SFA type and self-reported food intake. They found that "even-chain SFAs (these were the ones with a higher risk of developing type 2 diabetes) were positively associated with alcohol, soft drinks, margarine, and potatoes, and negatively associated with fruit and vegetables, and both olive oil and vegetable oil. By contrast, odd-chain SFAs generally showed positive associations with dairy products, cakes and cookies, nuts and seeds, and fruits and vegetables." This important distinction, thus, sheds some light as to why some saturated fat could actually be a good thing.

Dairy is a good example. There was a recent review article from 2012 on the influence of dairy product and milk fat consumption on heart disease and found "no association and in some cases an inverse relationship between the intake of milk fat containing dairy products and the risk of CVD, CHD, and stroke."

So, yes, there are nuances. This recent study puts forth an interesting hypothesis and supporting evidence for some of the conflicting messages around saturated fat as of late. Most importantly, however, I think it reinforces the need to understand and embrace nutrition's complexity. Food and nutrients are information for the body, with different types sending different messages. Nutrition advice and guidance should embrace these nuances, not cover them up.


Stay tuned for Part 2 where I will highlight some of the latest research on salt that challenges conventional thinking.

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