Beneficial, but not magical
As I hope to be able to show in a closer analysis of the study, he provision of a diet with a high fat content is beneficial for premenpausal obese women. It is yet not the magic solution to all their health and physique problems.
Figure 1: Macronutrient composition of the "high fat diet" (Silver. 2014)
It goes without saying that you'd expect the former to be unhealthy - it does after all have a pretty similar macro-nutrient composition as the previously cited high fat diets in rodent studies.
Consequently, you would probably not believe that the latter, i.e. a diet with max. 10% of the total energy from fat would produce results as they are listed in the "results"-section of the abstract to the paper at hand:
"Significant improvements occurred in fat oxidation rate (↑6%), body composition (%fat: ↓2.5 ± 2.1%; %lean: ↑2.5 ± 2.1%), inflammation (↓ IL-1α, IL-1β, 1L-12, Il-17, IFNγ, TNFα, TNFβ) and vascular function (↓BP, ↓PAI-1, ↑tPA activity)."If I am now telling you that the exact macro composition of the diet at hand had more resemblance with the classic HFD rodent chow (see Figure 1) , than with what you'd probably expect to see, when you hear about "a balanced high fat diet" in the title of a human study, this is hopefully not going to shatter your worldview altogether.
- Caveat #2: The high fat intake led to a significant decrease in energy intake -- Despite the presence of a pretty high amount of dietary carbs in the diet, the satiety effect of the diet (or the absence of the foods that made the women obese in the first place) led to a significantly reduced energy intake of ~10%, or 200kcal.
- It goes without saying that this is not a reliable calculation, but if we still do the math, this would amount to a total energy deficit of 22,400kcal over the whole study period and should result in a fat loss of 3.2kg. In practice, the ladies lost 33% more body fat (4.8kg on average), however - an unrealiable, but at least significant indicator that the reduction in energy intake is not the only, but still a significant contributor to both the fat loss and health effects of the 16-week study intervention.
Something you may not have read in the short abstract-based newsposts in the blogopshere...
...is that the important information that the actual aim of the present study was to test the hypothesis that body composition, inflammation and vascular function in obese premenopausal women would improve with a high fat diet (HFD) when - and this is where the magic is - "the type of fat is balanced as 1/3 SFA, 1/3 MUFA and 1/3 PUFA." (Silver. 2014).
In that, Silva and her colleagues from Vanderbilt University, the Northwestern University and the Tennessee Valley Healthcare System hypothesized that...
"[...]while consuming the balanced HFD, improvements in body composition, inflammation and vascular function would be greater when supplemented with 18C fatty acids - in proportion to degree of 18C fatty acid unsaturation." (Silva. 2014)In other words, the scientists expected to see the exact opposite of what the average low carber would propagate, i.e. greater improvements in body composition, inflammation and vascular function with a higher PUFA (omega-6, of all!) content of the diet.
To standardize the diets, the fat intake was modulated by the provision of 9 g/d of encapsulated pure stearate (18:0), oleate (18:1), linoleate (18:2) or a identically looking placebo supplement that were ingested on top of the high fat diet with the previously mentioned ratio of 50% fat, 30% carbohydrate and 20% protein. To further standardize fat intakes, all sources of fats including oils, spreads, nuts and seeds were provided weekly in pre-portioned containers.
|Figure 2: Fat intake (in % of total fat) in the four groups of this 16-week dietary intervention (Silver. 2014)|
|Figure 3: Changes in body composition (% of baseline) after 16 weeks on different "high fat" diets (Silver, 2014)|
The only inter-group differences that did achieve statistical significance were the reduction in interferon γ (↓74%) in the HFD+placebo, and the HFD+stearate diets and the significant effect of the
HFD+linoleate diet on the PAI-1 (↓31%) levels. The additional changes in vascular function as evidenced by an 8 mmHg reduction in systolic and a 6 mmHg reduction in diastolic blood pressure, as well as the minimal changes in the "suprisingly low" changes of the primary arterial compliance parameters, ie. the small and large artery elasticity index (SAEI/LAEI ml/mm Hg x 100) and the similarly disappointing improvements in flow-mediated dilatation (FMD) didn't show significant inter-group differences either.
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- Festa, Andreas, et al. "Relative contribution of insulin and its precursors to fibrinogen and PAI-1 in a large population with different states of glucose tolerance the insulin resistance atherosclerosis study (IRAS)." Arteriosclerosis, thrombosis, and vascular biology 19.3 (1999): 562-568.
- Heitmann, Berit Lilienthal, and Lauren Lissner. "Dietary underreporting by obese individuals--is it specific or non-specific?." Bmj 311.7011 (1995): 986-989.
- Keogh, Jennifer B., et al. "Flow-Mediated Dilatation Is Impaired by a High–Saturated Fat Diet but Not by a High-Carbohydrate Diet." Arteriosclerosis, thrombosis, and vascular biology 25.6 (2005): 1274-1279.
- Silver, Heidi J., et al. "Consuming a balanced high fat diet for 16 weeks improves body composition, inflammation and vascular function parameters in obese premenopausal women." Metabolism (2014).