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So, as "Battle of the mid-life bulge" says, slowing metabolism is no longer a valid reason to explain broader girth among 45 to 65-year-olds ( 12 March, p 38 ). Hormones and lifestyles change, and the advice to sleep more and limit stress, where possible, is welcome. But the what-to-do messages about expanding waistlines – …

A study mentioned in the article found that between the age of 45 and 65, most of us put on 0.5 to 1 kilogram of body weight per year. This rate of gain corresponds to about 0.5 to 1 per cent more energy intake than expenditure. Whether the overall increase in fat is due to …

We can't assume manufacturers will willingly get on board with a circular economy, given the temptation of planned obsolescence ( 12 February, p 38 ). I had a flat-screen TV fail. The maker quoted £300 for a new circuit board, also suggesting I could replace the TV. On opening it (I have some competence in …

The elephant in the room as far as waste goes is sewage. We produce huge amounts of it and it creates methane as it decomposes. In large sewage works, the methane is used to power machinery and to mix material by bubbling it up through new sewage. If surplus methane were sold and injected into …

Recent articles and letters have highlighted the importance of "waste not, want not" to reduce our environmental impact. Even more powerful is an approach we might call "want not, waste not": by reducing our desire for ephemeral or short-lived possessions for which we have no real need, we can have an even greater effect. Such …

Further to your report on concerns over Russia's nuclear weapons status, the "special regime of combat duty" that the country has elevated its nuclear readiness to is meaningless ( 5 March, p 7 ). It isn't an official category in Russia's nuclear level classification, meaning it was created to cause upset more than anything else. …

Alec Williams suggests we look for pixelation to see if our universe is a simulation ( Letters, 19 February ). That relies on the idea that the simulator's technology is similar to our own. Even if it isn't, we can see shortcuts being made by the simulator now. There is quantum indeterminacy, where the simulator …

My household is particularly keen on getting the real science behind climate change and the biodiversity emergency ( 26 February, p 26 ). Thanks for continuing to supply it in articles such as "Drowning in a sea of plastic". In it, Graham Lawton offered a balanced analysis – of hope tempered with political realism – …

I agree with Jingjing Liang's points on the shortcomings of current forestry management in a world where tree planting is seen as a climate solution ( 5 March, p 27 ). These problems can be seen in Europe. On a recent trip to Sweden, I discovered that the government is encouraging felling of thousands of …

That AIs may allow us to converse with whales, an idea raised in the book How to Speak Whale , would have been invaluable to Captain Kirk in the film Star Trek IV: The Voyage Home , in which the inability to respond to an alien probe trying to communicate with whales threatens Earth ( …