According to Drawdown, reducing food waste is the top individual action one can take to reduce one’s impact on climate change. Buffets tend to be quite wasteful and/or encourage serving older food a lot more than a la carte orders. There could be some exceptions, such as buffets in hotels where it’s included in the room rent and is a lot easier to plan for (the quantities) based on the number of guests and the guest…
Obesity has been linked to climate change in many studies. Here's a summary of one typical example: https://www.marketwatch.com/story/another-reason-to-combat-t... People in developed countries eating more food than they need is very wasteful, not just in food production, but the extra fuel needed to transport these people, the extra material needed to clothe these people, etc. Anybody who's overweight or obese can't…
For one, I don't think it's "as simple", and for two, the pattern "if you don't do X, you're not serious/credible/honest/worthy" is unhelpful.