acids) given to prevent heart attacks. In total, the meta-analysis included more than 600,000 participants from 18
Chowdhury and his colleagues found no significant
associations between dietary, circulating, or supplementary fatty acids and heart disease risk, with the exception
of dietary trans fats, which slightly increased risk in the five
studies analyzed. “Current evidence does not clearly support
guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated
fats,” the authors conclude. “Nutritional guidelines on fatty
acids and cardiovascular guidelines may require reappraisal
to reflect the current evidence.” A revision of the paper
retracted its initial conclusions on polyunsaturated acids
because of an erroneous analysis of omega-3 polyunsaturated acids, which were indeed associated with cardiovascular benefit. However, the study’s conclusions regarding
saturated fat remain unchanged.
Critics of the Krauss and Chowdhury reports point
out that the meta-analyses lumped together studies that
replaced saturated fat with polyunsaturated fat and those
that replaced saturated fat with carbohydrates. “When you
look at meta-analyses that actually distinguish between the
replacement components, there’s a clear benefit of replacing saturated fat with polyunsatured fat but not of replacing
saturated fat with carbohydrates,” says Alice Lichtenstein,
professor of nutrition science and policy at Tufts University and vice-chair of the 2015 Dietary Guidelines Advisory
Committee. In other words, saturated fat may be bad for
you compared with polyunsaturated fat, but its negative
effects could be masked by the fact that carbohydrates
are even worse.
Krauss agrees that the overall dietary context is important to consider when interpreting these studies. When people are asked to lower their intake of one nutrient, such as
saturated fat, they compensate by increasing their intake
of another, such as carbohydrates. “In the context of our
findings we tried to explain that saturated fat per se cannot easily be connected to adverse effects,” says Krauss.
“We’re trying to broaden the discussion from this monomaniacal focus on one single chemical in foods, saturated fat.”
Time for a change?
With an updated version of the Dietary Guidelines for Americans set to be released in the third quarter of 2015, some
researchers were hopeful that, given new evidence over
the past five years, saturated fat would be at least partially exonerated. However, the Scientific Report of the
2015 Dietary Guidelines Advisory Committee continues to
identify saturated fat as a “nutrient of concern for overconsumption” that should be limited to less than 10% of
total calories. Although the federal government will have
the final say on the Dietary Guidelines, it is unlikely that
the guidelines will diverge significantly from the scientific
report of the committee.
Krauss considers it a good sign that the Dietary Guidelines Advisory Committee hasn’t recommended cutting
saturated fat even further, down to the Draconian 5–6%
of total calories suggested by the American Heart Association. “Ten percent is a reasonable amount of saturated fat,”
he says. “But rather than the notion that people should be
Fig. 2. Effects of fatty acids on LDL and HDL cholesterol. (Left) Saturated and trans fats increase the serum levels of LDL, or
“bad,” cholesterol. (Center) Saturated and unsaturated fatty acids increase HDL, or “good,” cholesterol. (Right) Unsaturated
fats decrease the ratio of total cholesterol to HDL, indicating a reduction in heart disease risk. Trans fats increase this ratio,
while saturated fats do not substantially increase or decrease the ratio. Credit: Gerald McNeill, prepared from data in Mensink, R. P., et al. , “Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum
lipids and apolipoproteins: a meta-analysis of 60 controlled trials.” Am. J. Clin. Nutr. 77: 1146-1155, 2003.
continued on page 377