It will have escaped nobody's attention that the West is fully submerged in an obesity epidemic. New research collates contradictory evidence on low-fat diets and their success rates.
According to the Centers for Disease Control and Prevention (CDC) more than 1 in 3 (34.9%, or 78.6 million) US adults are obese.
The CDC estimate that the annual medical cost of obesity in the US was $147 billion in 2008. They calculate that the medical costs for obese people were $1,429 higher than those of a normal weight.
This surge in weight gain has attracted the attention of researchers and health care specialists alike - and for good reason.
There is a certain urgency in halting or at least slowing this upward trend. Results of research into the best, most effective or longest-lasting diet regime are regularly contradictory.
Multiple factors - including the type of participant, the length of trial and the level of interaction with participants - make drawing conclusions difficult.
'No good evidence' to recommend low-fat diets
Fats have more than twice as many calories per gram as proteins and carbohydrates. This fact makes fat a prime target in the quest to reduce and control weight. The logic goes that simply reducing fat intake will lead to weight loss.
Low-fat diets have been investigated in numerous ways over the years. The current study, lead by Deirdre Tobias, PhD, from Brigham and Women's Hospital and Harvard Medical School in Boston, MA, aimed to collate and analyze the contradictory results.
The results from this meta-analysis, perhaps surprisingly, point in the opposite direction of common sense. Tobias puts it succinctly:
"There is no good evidence for recommending low-fat diets."
The meta-analysis, one of the largest of its type, includes 53 studies and a total of 68,128 adults. It compares the efficacy of low-fat diets with diets that do not restrict the amount of calories derived from fats.
Tobias and colleagues carried out a systematic review and meta-analysis of all randomized trials comparing the effectiveness of low-fat diets (compared with other diets) at improving weight loss over a minimum duration of 1 year.
The team searched Medline, Embase, Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews to find eligible trials.
The importance of intervention
The analysis took into account the intensity of the diets, which ranged from participants simply receiving general instructions at the start of the program, to intensive programs that included counseling sessions, meetings with dieticians, food diaries and cooking lessons.
Of the 53 eligible trials, 19 compared a low-fat diet with a control group who maintained their normal diet. The low-fat groups underwent multiple interventions including interaction with research staff, whereas the control group were, more or less, left to their own devices.
In these examples, the effect of the diet alone cannot be ascertained; the diet is not an independent contributor to the outcome.
In this regard, the team controlled for the level of intensity. Diets where participants were given more support and guidance were generally more successful than those in which little support is given. The researchers note:
"Low-fat interventions were favored only in comparison with interventions of lesser intensity, particularly those in which controls were only asked to maintain their usual diet."
Tobias sums up the study's counterintuitive findings and gives future food for thought:
"The science does not support low-fat diets as the optimal long-term weight loss strategy. To effectively address the obesity epidemic, we will need more research to identify better approaches for long-term weight loss and weight maintenance, including the need to look beyond differences in macronutrient composition - the proportion of calories that come from fat, carbohydrate, and protein.
Long-term adherence is critical for the success of any dietary intervention, and one should also take into account other long-term health effects of their dietary choices."
Another finding of the team, which is both interesting and slightly disheartening, concerns the general success of the interventions as a whole. The average weight loss in all groups included in the study after a median 1 year of follow-up was just 2.7 kg.
With obesity still very much in media and medical spotlights, further trials, as outlined by Tobias, will steadily bring us more insight into one of the largest challenges that Western medicine currently faces.