Cautionary AdviceI enjoyed Tad Friend’s witty and entertaining piece about the fascinating world of anti-aging (“Live Long and Prosper,” August 11th). I am not a biohacker, but, like the people Friend writes about, I am very particular about my diet and exercise. I’ve made changes to my training routine and diet, and, since then, I’ve felt stronger, sharper, and more nourished. Matigan KingNew York City•Letters should be sent with the writer’s name, address, and daytime phone number via e-mail to themail@newyorker.com. Letters may be edited for length and clarity, and may be published in any medium.