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).
Fat
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.
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.
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