London also points out that even if something is true, it doesn’t necessarily mean you should do it. For example, there are numerous studies indicating that intermittent fasting (going from eight to 24 hours without eating anything, sometimes several days a week) may in fact put you in a state of ketosis, where fat is used for energy instead of sugar in the form of glucose. But the other thing low blood sugar does is fuzz your vision (not ideal if you read a lot), prevent you from focusing at work and mess with your ability to exercise. I have fasted. Probably you have too. Here’s the SparkNotes revelation: You feel bad; then you feel really really good; then you want to die; then you Hoover up whatever’s in the refrigerator.

When an author starts off with “I’m here to tell you …” I’m pretty sure the rest of that sentence will be worthless. And here, in Jonathan Bailor’s THE SETPOINT DIET: The 21-Day Program to Permanently Change What Your Body “Wants” to Weigh (Hachette, $27), is the rest of that sentence: “you can be a member of that exclusive ‘club’ of naturally thin people.”

Super.

Still, what’s more seductive than the idea that we can change our setpoint: the number on the scale, give or take 10 or 15 pounds, that our body seems to return to again and again? Bailor has come up with the SANE diet, which suggests that not all calories are created equal and that in fact different food calories have varying degrees of Satiety, Aggression (meaning, how quickly those calories flood your body with glucose), Nutrition and Efficiency. You can become a fat-burning machine by chucking some of the foods — basically, anything that makes life worth living — and consuming a lot more of others. (Did someone say lean protein and veggies?) Although Bailor isn’t a medical doctor — in fact, he created fitness videos at Microsoft — there’s some solid science behind what he says. Depending on what you eat and when you eat it, you can make a difference. The problem? It’s the kind of eating that demands you think of food more as fuel than, say, a source of pleasure. And you have to do it forever. I know I couldn’t. But here’s my favorite Bailor factoid. In a chart on all the things that increase your setpoint — that is, keep you at a higher weight — along with starchy, sugary foods and diet pills, he lists the news. I’m confident that when the Southern District of New York releases all it knows about Trump’s various businesses, my pants will be looser.

I admit Bryan Kozlowski’s THE JANE AUSTEN DIET: Austen’s Secrets to Food, Health and Incandescent Happiness (Turner, cloth, $31.99; paper, $16.99) is probably better as a literary romp than as a dieting tome. But Austen fans and superfans (ahem) will enjoy being reminded of how smart she actually is about our health, and how she uses food, eating and exercise as shorthand for character. Kozlowski contends that Austen’s embrace of body diversity (Anne Elliot in “Persuasion” is desirable and petite; Lydia Bennet is equally alluring as a curvy, “stout, well-grown girl”) and subtle recognition of the mind-body connection (good health and happy spirits are intimately intertwined) put her ahead of her time. And in “Austenworld,” only her nonsensical characters become romantically attached to food (Dr. Grant, the clergyman in “Mansfield Park,” lived to “eat, drink and grow fat”). There are Regency-era recommendations for exercise (all that walking) and tinctures for good health that have at least some basis in reality. (Dandelion tea, popular in Austen’s novels for “liver disorder,” has been shown to maintain the proper flow of bile.)

Perhaps most delightful is the reminder of a classic exchange in “Pride and Prejudice” that every woman should emulate. When Darcy and Lizzie Bennet are at a party and he comments to his friends that her body is “tolerable, but not handsome enough to tempt me,” Lizzie’s reaction is to crumple into a ball and cry. Oh no, wait, it’s not! Here’s her real reaction: She thinks he’s ridiculous. And then she laughs with her friends.