Chowdhury et al, More forests & more trees and more "Eureka!" moments with cheese.

Like Siri-Tarino et al, Forests & Trees and "Eureka!" moments, Chowdhury et al is a meta-analysis of many studies. See Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis. I don't have access to the full study, but Google Image Search found Figure 2.

From http://annals.org/data/Journals/AIM/929862/6ff2_Figure_2_RRs_for_coronary_outcomes_in_prospective_cohort_studies_of_circulating_fatty_acid.jpeg

All saturated fatty acids have a RR for CHD of 1.06 (95% CI 0.86 - 1.30).
∴ There's no association between saturated fat intake and the RR for CHD.

Before VLC'ers do a dance of joy, consider the Forest plot for individual saturated fatty acids.
Palmitic acid has a RR for CHD of 1.15 (95% CI 0.96 - 1.37).
Stearic acid has a RR for CHD of 1.23 (95% CI 0.93 - 1.61).

Red meat & saturated fats synthesised by DNL aren't looking too good. However...
Pentadecanoic acid has a RR for CHD of 0.94 (95% CI 0.67 - 1.32).
Margaric acid has a RR for CHD of 0.77 (95% CI 0.63 - 0.93).
Pentadecanoic acid and Margaric acid combined have a RR for CHD of 0.81 (95% CI 0.62 - 1.06).

What are Pentadecanoic acid & Margaric acid found in? The clue's in the title:-
Say cheese: saturated fat in dairy may protect against diabetes.

The article in the Telegraph is actually referring to Differences in the prospective association between individual plasma phospholipid saturated fatty acids and incident type 2 diabetes: the EPIC-InterAct case-cohort study.

Of the omega-3 fatty acids...
Eicosapentaenoic acid has a RR for CHD of 0.78 (95% CI 0.65 - 0.94).
Docosahexaenoic acid has a RR for CHD of 0.79 (95% CI 0.67 - 0.93).
Eicosapentaenoic acid and Docosahexaenoic acid combined have a RR for CHD of 0.75 (95% CI 0.62 - 0.89).

Of the omega-6 fatty acids...
Arachidonic acid has a RR for CHD of 0.83 (95% CI 0.74 - 0.92).

Of the trans-fatty acids...
Trans-oleic acid has a RR for CHD of 1.20 (95% CI 0.39 - 3.73).
Trans-linoleic acid has a RR for CHD of 1.36 (95% CI 0.83 - 2.22).

Siri-Tarino et al, Forests & Trees and "Eureka!" moments.

Here's Fig. 2 from Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease:-

Risk ratios and 95% CIs for fully adjusted random-effects models examining associations between saturated fat intake in relation to coronary heart disease and stroke.

The above "Forest" plot has a subtotal RR of 1.07 (95% CI 0.96 1.19). The overall conclusion is that there's no association between saturated fat intake and the RR for CHD. Hmmm.

I looked at the data in Table 3. Of the 16 studies contributing to the CHD results, only 3 of them specify high sat fat intakes over a wide range. The results from these 3 studies are as follows:-

Pietinen et al: RR=0.93 (95% CI 0.6, 1.44).
Mann et al: RR=2.77 (95% CI 1.25, 6.13).
Boniface et al: Pooled RR = 1.37 (95% CI 1.17, 1.65).

The results from Pietinen et al are statistically-insignificant (95% CI values are way above & below 1) with an overall slight protective effect. The results from Mann et al have a RR >> 1 with both 95% CI's >1 and the results from Boniface et al have a RR >1 with both 95% CI's >1.

Other studies either have sat fat intakes varying from very low to low, or specify mean/median sat fat intakes without values for highest & lowest tertiles/quartiles/quintiles etc. Other studies have results that are statistically-insignificant.

However, there are some studies that show a slight protective effect of small amounts of sat fats. How come?

Thanks to George Henderson, I had a "Eureka!" moment. He posted a link to Dietary intake of saturated fat by food source and incident cardiovascular disease: the Multi-Ethnic Study of Atherosclerosis.

Here's Fig. 1 from that study.

HRs and 95% CI's of CVD risk according to quintiles of energy-adjusted SF from different sources (n = 5209).

The Meat SF plot has a net positive slope (bad news, but the range of intake is very small), the Butter & Plant SF plots are random, but the Dairy SF plot has a net negative slope (good news). Dairy saturated fats in amounts of up to 10g/day are protective against CHD. As the Dairy sat fat intake is too small to have a significant effect on lipids, what's the mechanism? I think that it's Vitamin K2. See Chowdhury et al, More forests & more trees and more "Eureka!" moments with cheese.

When you average out the results from all studies, the result is null. This is data dilution statistics.

EDIT: See also Study: Saturated Fat as Bad as Sugar!