Does Fat Make You Fat? A Review of Scientific Studies.

The intention of a review by Shikany et al. (Shikany. 2010) was to answer a bunch of questions surrounding the "war" that has been raging between low and high fat dieters in the past months, even years. Let me anticipate the result: there is no conclusive answer to the question, whether fat will make you fat. Not yet...!?

A comprehensive review of electronic citation databases was conducted to identify studies related to  the following questions:

1. What are the effects on body weight and body fat if the prescribed proportion of ingested energy from fat under isoenergetic conditions is altered? 
2. What are the effects on body weight and body fat if the prescribed proportion of ingested energy from fat under ad libitum but confined conditions is altered?
3. What are the effects on body weight and body fat if the prescribed proportion of ingested energy from fat under ad libitum, non-confined conditions is altered?
4. What are the effects on body weight and body fat if the prescribed proportion
   of ingested energy from fat in a defined subset of the diet— a  daily snack—under ad libitum, non-confined conditions is altered?

Other than the research questions, the results are less concrete:

The results indicated that whether “fat is fattening” depends on exactly what one means by the question. It is apparent that under conditions of energy deficit, high-fat diets lead to greater weight loss than low-fat diets, but under ad libitum feeding conditions, instructing persons to follow a low-fat diet promotes loss of body weight and body fat.

Shikany et al. summarized their data on diet and high vs. low fat diet in the table shown below:

Table 1: Difference in body fat change in response to high- or low-fat isoenergetic diets (question 1)

With regard to the remaining questions they write:

For one question, studies were few but convincing that altering the proportion of energy from fat in daily snacks has no effect on weight, while for another there were not enough studies available to answer the question with confidence.

As they state in their conclusion the data on low fat vs. high fat dieting or rather eating (i.e not restricting calories) appears to provide little orientation and "general recommendations to reduce dietary fat to promote weight loss or maintenance in all circumstances may merit reconsideration".