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Which is better? High fat or low fat diets: appetite, weight loss & hedonics

The age old debate

High fat vs low fat diets have been heavily debated in the past 2 decades. One side is arguing high fat intakes are better for fat loss whereas, the other side is arguing low fat is better. Before we begin, it is important we talk about fat in context. This article will just be referring to quantities of fat with regards to weight loss, appetite & food hedonics. If we were to talk about health we would need to dive into much more detail about the different fatty acid types. With that out of the way, is high fat or low fat better?

 

Macronutrients have a hierachical effect on appetite.

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To begin with, macronutrients are vastly different in chemical structure and can be divided into 3 main groups: protein carbs & fats. It's well known that each macronutrient vary in energy content but many people aren't aware of it's effects on our appetite.

It’s been well established in the literature that protein has strongest ability to suppress our appetite, we see a similar effect with carbohydrates but fat does the poorest job. So what does this mean? What can we do with this information?

The Study: Differing effects of high-fat or high-carbohydrate meals on food hedonics in overweight & obese individuals

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The study wanted to investigate the effect of high fat low carb (HFLC) and low fat high carb (LFHC) meals appetite and various other end points. Participants were divided into two groups; group 1 had to consume a HFLC diet and group 2 had to consume a LFHC diet.

After each meal they measured the end points: appetite, energy intake, explicit liking & implicit wanting for various foods. After the day had finished, each group had a 2 day “washout” period to make sure the intervention on day 1 does not interfere with the results for the next part of the study.

On the 2nd test day, the participants had to crossover to the other intervention. This is called a parallel cross over design. It essentially exists so that each group acts as their own control. It is also very useful to increase the statistical power of results with small study groups.

The study gets more interesting.

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Food & meals in both groups were matched in calories. Apart from the fat to carbohydrate ratios the calories were identical. Each group was then told they could consume as much food as they liked – ad libitum.

The results were very interesting, the HFLC group consumed far more calories for breakfast, dinner and across the day. Perhaps there is some sort of appetite suppressing factor that carbohydrates elicit but is absent in fats (and there is but will not be discussed in this article).

In another part of the study, they matched the energy intake – meaning they were only allowed to eat the same amount across both interventions. What they found was that participants  were more satiated immediately and 2 hours after ingesting a LFHC meal compared to a HFLC meal. They were also less interested in having “fatty” food after.

To sum up the results, when comparing HFLC to LFHC, LFHC reduced energy intake, increased satiety, helped suppress “fatty cravings” and the results were consistent with many other findings in the literature. It seems that following a low fat diet is a realistic and an easy way to lose weight through satiation & a reduction in energy intake. However, there are limitations to this study; the sample was small (a larger study group would add statistical power to the results), participants were only overweight & obese individuals (what about lean individuals?) and the female menstrual cycle wasn’t factored in (cravings for food, weight & metabolism fluctuates).

How would this stack up to high protein diets? Body composition was not discussed. There are many other factors that will affect a persons fat intake so the results need to be put into context.

 

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