We all know that fat is fattening right? (It is called fat, after all.) But not so fast, because as I detail here, for fat to get ‘fixed’ in the fat cells, a substance known as glycerol is required. Glycerol itself is supplied from a substance known as alpha glycerol phosphate (also known as glycerol-3-phosphate), which itself comes from the metabolism of glucose (carbohydrate). It should also be borne in mind that for sugar to get into the fat cells in the first place insulin is required, and this hormone is secreted most plentifully in response to the ingestion of carbohydrate.
The insulin secreted in response to carbohydrate (but not fat) also affects enzymes in a way which inhibits fat breakdown and enhances fatty deposition in the body.
So, one line of argument goes that eating a glut of carbohydrate (not fat) is what is truly fattening. It’s not a new message: most of us will have heard this concept before if we’re at all familiar with the work of the late Dr Robert Atkins, and at least some new life has been breathed into this idea through the work of Gary Taubes (author of Good Calories, Bad Calories/The Diet Delusion).
The idea that fat may not be intrinsically fattening received some support this week in the form of a study which assessed the relationship between dietary fat levels in almost 90,000 European adults and changes in body weight [1]. Individuals were followed for several years.
This study looked at the relationship between total fat intake and weight change, as well as the relationship between different types of fat (saturated, unsaturated and monounsaturated) and weight change too.
Once appropriate so-called ‘confounding factors’ such as dietary and lifestyle factors were taken into account, the authors could find no association between total fat intake or intake of any specific type of fat and weight change. They concluded We found no significant association between the amount or type of dietary fat and subsequent weight change in this large prospective study. These findings do not support the use of low-fat diets to prevent weight gain.
Epidemiological studies of this nature are not necessarily the best way to adjudge the effect of dietary fat on body weight. The acid test is really to, say, put people on low-fat diets and see if they successfully lose weight in the long term. A major review of relevant studies showed that, by and large, they don’t [2]. This study, undertaken by scientists from the respected Cochrane Collaboration, was withdrawn in 2008. The reason? It was out of date, and that the authors had no intention of updating it.
There are plenty of studies out there that might be viewed as ‘out of date’, but if there’s no new evidence to challenge their findings then, as long as the research has been performed appropriately and honestly, then they should surely stand. Back in 2002 the evidence clearly showed that low-fat diets are not effective for the purposes of weight loss, and the reality is nothing has changed now.
Some might argue that while reducing fat intake is ineffective for weight loss, it might however be more effective regarding fat loss specifically. This question was considered by a major review conducted at the Harvard School of Public Health in the USA [3]. After reviewing literally dozens of studies which examined the relationship between fat eating and body weight, as well as the effectiveness of low-fat diets, the authors concluded that Diets high in fat do not appear to be the primary cause of the high prevalence of excess body fat in our society, and reductions in fat will not be a solution.
For individuals seeking to shed fat effectively in the long term, getting control of insulin levels is often key. This generally means cutting back on carbs, particularly those most disruptive to blood sugar and insulin levels such as those with added sugar and starchy staples such as bread, potatoes, rice, pasta and breakfast cereals. Another huge benefit associated with the eating of such a diet is that people often end up eating less, quite spontaneously and, importantly, without hunger.
References:
1. Forouhi NG, et al. Dietary fat intake and subsequent weight change in adults: results from the European Prospective Investigation into Cancer and Nutrition cohorts. Am J Clin Nutr 14 October 2009 [epub ahead of print]
2. Pirozzo S, et al. Advice on low-fat diets for obesity. Cochrane Database Syst Rev. 2002;(2):CD003640
3. Willett C, et al. Dietary fat is not a major determinant of body fat. Am J Med. 2002;113(9B):47S-59S
