If You Must Have A Dietary Culprit, At Least Pick The Right One

Let’s say you decide to have yogurt for a snack, and let’s say that yogurt is the sweetened kind made with whole milk. Is this a healthy choice? Many nutrition experts might agree that it’s not. But they might disagree as to how it could be healthier.

Some might want to cut the fat. Fat—particularly saturated fat like that found in dairy products—has been a dietary concern for decades. Beginning in the 1950s, American scientist Ancel Keys developed a theory of fat, and then saturated fat, as a cholesterol-raising promoter of heart disease.

Keys’ theory was embraced by the American Heart Association (AHA) and ultimately by the U.S. government whose 1977 Dietary Goals unambiguously recommended restricting fat, particularly saturated-fat, in the diets of Americans.

However, the evidence supporting fat restriction was weak. If we could travel back in time to systematically evaluate all the evidence available when the Dietary Goals were adopted, we would find precisely no experimental trials (the gold standard for determining cause and effect in science) to show a health benefit of restricting saturated fat in the diet.

Of course that was 40 years ago. Since that time science has progressed and dietary guidance has evolved. But the government’s current Dietary Guidelines for Americans still recommend restricting saturated-fat intake despite the fact there are still no scientific trials to show that people live longer or healthier by doing so.

Conversely, there is compelling evidence that trying to avoid saturated fat may be contributing to obesity, diabetes, and heart disease—exactly what we were hoping to avoid by avoiding saturated fat. When saturated fat was restricted in foods and diets, something more harmful came in to take the place: sugar.

Interestingly, around the same time Ancel Keys was making his case against fat and saturated fat in America, the United Kingdom’s John Yudkin was making a similar case against sugar. Yudkin was able to show that heart disease tracked even better with consumption of sugar than with consumptions of fat.

Yet Yudkin and Keys could both find support for their theories in observational studies because people eat foods, not food constituents, and the dietary sources of fat are also often dietary sources of sugar (e.g., sweetened full-fat yogurts).

Although the 1977 Dietary Goals for Americans did  recommend restricting sugar in addition to restricting fat and saturated fat, the central message of the document—and of subsequent Dietary Guidelines published in the years since—was to replace dietary fat with dietary carbohydrate.

People were advised to eat more starch (chemically just long chains of sugar) in place of foods high in fat. The results were disastrous. Added sugars and starches replaced fat and saturated fats in the American diet, and diabetes and obesity rates skyrocketed.

Sugar—not saturated fat—has been found consistently to track with increasing rates of obesity and diabetes. And those who consume more sugar—not saturated fat—are at greater risk of heart disease and heart-related deaths.

Yet even today, guidelines like those for Lifestyle Management to Reduce Cardiovascular Risk (co-sponsored by the AHA) focus intensely on saturated fat, recommending it contribute no more than 5-6% of total calories. The same guidelines make no specific recommendation about sugar (other than general advice to “limit intake”).

In three recent academic papers, we review some of the evidence implicating the intake of added sugars in obesity, diabetes, and heart disease. Thus, returning to the sweetened full-fat yogurt example, the healthier snack would be an alternative variety that comes without added sugar. It would not be a persistently sugared low-fat or non-fat version.

But more importantly, the focus of dietary advice and attention should be on whole foods (like yogurt), not isolated food constituents (like saturated fat). Yogurt, as a food, is quite different from other food sources of saturated fat (e.g. processed meats), and saturated fat itself is actually a diverse class of compounds.

Sugars are also a diverse class of compounds. Different dietary sources will have different effects.

To the extent any good can come from focusing on food constituents, we should at least pick the one most consistently associated with harm as an all-around dietary culprit. Added sugars of all types are bad. Fat, and saturated fat in aggregate, is not. Dietary guidelines should make this clear.

http://www.forbes.com/

Graham