The Evidence for diets - Part 2

In Part 1 we looked briefly at the absurd history of dieting and why it doesn't make sense on a common sense level. In Part 2 we are going to look at what science says about obesity, weight and dieting. Why have we been made to believe that weight loss dieting is for our best interests. And just how wrong are we? Let's explore. 

Belief: Body fat increases mortality risk

Evidence: Body fat very weakly predicts longevity 

Most epidemiological studies find that people who are overweight/moderately obese live as least as long as normal weight people. In fact, the greatest longevity is people in the overweight category. Being very underweight is more of a risk factor to longevity than any other weight.

Belief: Body fat increases risk of morbidity

Evidence: While obesity is associated with increased risk of chronic conditions it is not a cause and effect relationship

Unfortunately, studies looking at weight and disease rarely acknowledge health factors such as physical activity, psychological wellbeing, nutrient intake or socioeconomic status. It is likely that these other factors increase or decrease disease risk rather than weight. For example, in individuals who have lost and regained weight over and over have increased inflammation leading to cardiovascular disease and diabetes. Therefore the association between weight and health is attributed to weight cycling rather than body fat. 

Belief: Anyone who is determined can lose weight and keep it off through appropriate diet and exercise. 

Evidence: Long term studies show that the majority of individual regain most if not all the weight that was lost. 

The womens Health Initiative followed women 8 years after they started a low fat diet and found that there was almost no change in weight and even a slight increase in abdominal fat even though they continued to eat less and exercise more for the duration of 8 years. It has been found that weight loss peaks at 1 year after starting a dieting and after that weight is refined to the point of little change from the beginning. Unfortunately most diets do not outline this otherwise no one would start them!

Belief: The pursuit of weight loss is a practical and positive goal 

Evidence: Dieting reduces bone mass, increases psychological stress and cortisol production, increases risk of chronic disease and rheumatoid arthritis. 

An emphasis on weight loss causes preoccupation with weight, body shape and food which is a contributing factor to anxiety and eating disorders. In fact body dissatisfaction is linked to lower levels of physical activities and increased levels of binge eating. On top of this, there is the demotivating effects of weight discrimination that lead to increased quantities of food eaten, avoiding medical care and exercise.

Belief: The only way for overweight and obese people to improve health is to lose weight

Evidence: Weight loss improving health is an unproven theory as there are little methods to determine this in the longterm. 

Most health indicators (blood pressure, blood lipid levels, energy levels, psychosocial health) can be improved by changing behaviours regardless of weight. Studies looking at those with diabetes found improvements in blood glucose levels when exercise was increased and eating low GI foods with no weight loss.  

Conclusion

Being weight loss focused is not working to produce healthier, happier people and instead is contributing to food and body obsession, decreased self esteem, weight cycling, weight discrimination and distraction from wider health goals and definitions. 

Reference: Weight Science: Evaluating the Evidence for a Paradigm Shift, Nutrition Journal 2011.