Medical students are taught that half of the facts they learn are not true – we just don’t know which half. Some of our most widely believed medical facts are based on almost no evidence at all.
Is being slightly overweight (with BMI 25 – 30) healthier?
- Health weight range is not based on solid evidence (e.g. a significant study undertaken on many thousands of people or several such studies) with clearly defined basic categories i.e. BMI greater than 30 [Body mass Index; the ratio of body weight to the square of body height (kg/m2)]. Meta-analysis, is usually the holy grain of medical research, to provide the definitive answer to a scientific question.
- When the WHO (World Health Organisation) experts gathered to define obesity, BMI 30 has been chosen arbitrarily. Yet, obesity in middle age can reduce the risk of a person developing dementia later in life; to be overweight may well be healthier than to have normal weight. People who are considered overweight, with BMI 25 – 30, live longer. If methods of defining cut-off points in healthcare are largely arbitrary, it come as no surprise when the health definitions do not stand up to scrutiny.*
In the ageing face, intuitively extra weight seems to add plumpness to the facial structures temporarily but research shows that thicker subcutaneous fat layer is significantly linked to reduced dermal elasticity and increased sagging severity at the lower cheek in Japanese population [Ezure T, Amano S, 2010].
Clinically, I see yo-yo diets and rapid weight loss exacerbating ageing concerns more than higher BMI.
In terms of the skin barrier function that often translates to dry, flaky skin, redness & sensitivity, the “tight winter skin feel” – we have mixed & inconclusive results of tree small studies carried out at the forearm – not the face.
- Loffler et al (2002) studied the relationship between BMI and the physiological function of the skin, showing that higher BMI lead to higher Trans-epidermal Water Loss (TEWL) and less functional skin barrier.
- Puch et al (2008) found that normal weight participants (BMI < 25) responded better to supplementation than overweight participants (BMI >25). In the obese, skin barrier was weaker and skin colour increased in redness.
- In contrast, Guida et al (2010) observed reduced TEWL rate indicating better skin barrier in the obese compared to normal weight participants (BMI 18.5-24.0 kg/m2).
More research is needed to clarify how BMI impacts on the ageing female face. The patterns of different skin parameters require detailed mapping; there seem to be minor changes of TEWL but e.g. a clear increase in skin surface pH during the course of life [Trojahn et al (2015)]. More about facial maps in my next blog..
*Sunday Times 12th April 2015, Sorry, Madam, You really must eat more cakes by GP Malcolm Kendrick. Based on extracts from his book Doctoring Data: How to sort out medical advice from medical nonsense.