Before I go off Twitter for a week or so to get on with proper work it might be helpful, at least for some correspondents, to review a few pretty well established facts
1. Obesity has become more common in the recent past (precise trajectories depend on which country) \\

2 This is very unlikely to have anything to do with genetics
3. This is most likely to do with an obesogenic food environment combined with a reduced need to expend energy in work and domestic life
4. In all societies, and at all times, some people have been obese and some not

5. Whenever it has been measured the heritability of "fatness" is very high. Most clearly through studies of identical vs non identical twins. Even more strikingly with studies of separated twins brought up in different families.

6. From the 1990s, mutations disrupting the function of specific genes were found to be causative in certain families with severe obesity
7. It became increasingly clear that these genes were all functioning in a circuit in the hypothalamus of the brain controlling appetite

8. Later, when genetic tools became powerful enough to study common genetic variants in very large populations some such variants were found to reproducibly associate with "fatness"
9. Notably, the genes they were located in were mostly expressed in the brain

10, The specific common variants discovered to date only explain a modest percentage of the "heritability" of "fatness" .
11. That's not surprising. Humans are hugely genetically variable. Many of us carry recently emerged variants unique to members of our own recent family

12, The practical implications of these discoveries are many and varied
13. Severe early-onset obesity resulting from severe mutations in certain of these genes can now be treated effectively by therapy directed to those defects.
14. More examples of this are likely to follow

15. The improved knowledge of the "wiring diagram" of appetite control that genetics provides us with will help us design anti-obesity therapies that are more effective and safer

16. The increasing knowledge of the biological basis for differential susceptibility of ppl to obesity should make us less judgmental and more supportive of ppl who struggle with obesity

17 This should translate into better health care and less social discrimination for people who happen to be obese

To repeat. We need to work to change the env. to make it less obesogenic. However, unless we create chronic famine (clrly undesirable!) there will always be ppl with obesity, Our increasing knowledge of the biology behind this will help us design more effective ways to help