Friday, February 17, 2006

What Does Saturated Fat do to your Blood Pressure?

With all the hubub surrounding the null findings for risk reduction with a low-fat diet in the WHI Dietary Modification Trial, some other interesting research is being overlooked. This month, the American Journal of Clinical Nutrition published Effects of dietary saturated, monounsaturated, and n–3 fatty acids on blood pressure in healthy subjects.

Researchers recruited 162 healthy subjects who were randomly assigned to one of two diets - high in saturated fat (SFA) or high in monounsaturated fat (MUFA). Both diets were isoenergetic (meaning enough calories to maintain the participants weight) and contained similar macronutrient distribution - 37% total fat, 15% protein and 43% carbohydrate.

Both groups were then randomized into two more groups - one group in each diet would also take supplements of omega-3 fatty acids while the other simply took a placebo.In the high saturated fat dieters, saturated fat intake was targeted to be 17% of energy daily, MUFA another 14% and PUFA 6%. In the high MUFA dieters, saturated fat was targeted to be 8% of energy, MUFA 23% and PUFA 6%.

The stated objective of the researchers: to evaluate the effects of different types of dietary fat on BP in healthy subjects.

Their conclusions: Changing the proportions of dietary fat by decreasing SFAs and increasing MUFAs decreased diastolic BP. Interestingly, the beneficial effect on BP induced by fat quality was negated by the consumption of a high total fat intake. The addition of n–3 fatty acids to the diet had no significant effect on BP.

Nary a word about how the high SFA group did.

Do you want to know? I did, so I took the time to read through the full-text and data tables....imagine my surprise when tucked in there was a statistically significant change in those eating a high saturated fat diet with more than 37% of their calories from total fat!

While it was true that there was a statistically significant decrase in diastolic blood pressure (your lower number) with the high MUFA diet in those who didn't reach 37% of total calories from fat each day (p = 0.016), there was NO statistically significant change in systolic pressure (p = 0.152).

Sorry, no dice - high MUFA in a diet with 37% or less fat didn't do all that much...

In reading the abstract conclusion, you'd probably walk away thinking the SFA group did poorly, huh?

Well, get a load of this....

In those consuming MORE than 37% of their total calories from fat, with a high saturated fat intake their decrease in diastolic blood pressure was significant too (p = 0.014) - more significant than those eating less than 37% total calories on the high MUFA diet (p = 0.016).

Not only that, but those eating more than 37% of their total calories from fat on the high SFA diet almost reached statistical significance with the decrease in their systolic blood pressure (p = 0.0524).

I say "almost" because the "p value" technically remains greater than 0.05, which is what you go by with a CI of 95%.

I didn't round the result - if I had, I could have deceived you and just said it was just 0.05, technically correct - but that wouldn't be all that honest, would it?

Do you want to know what else, besides saturated fat, the dieters eating the high SFA diet consumed? Cholesterol. Yup - more cholesterol - 322mg per day (+/-91mg).

Just one more example of how what's stated in the abstract isn't the whole story behind a study and it's data.....


  1. Anonymous12:33 AM

    hey guys,
    i would just like to let you know...
    that this information is very unuseful!
    thank you for your time <3

  2. Anonymous7:29 AM

    Based on the comments above it seems like the study wasn't particularly well designed, or rather it was designed to show that MUFA is better than SFA. You can't do a useful study on the affects of eating a high saturated fat diet when you also include lots of carbohydrates. I think there is plenty of evidence that lots of any fat with lots of carbohydrates is not a good idea. What this study fails (presumably on purpose) to evaluate is the effect of a high saturated fat, low carbohydrate diet. My expectation is that it would reduce blood pressure (at least in people with high bloody pressure) by a very statistically significant amount. I want to see a study entitled: What Does Carbohydrates do to your Blood Pressure? And then another one: What Does Hydrogenated Fat do to your Blood Pressure? Hopefully the study controlled for hydrogenated fat, otherwise the results are pretty much useless.