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In my bestseller How Not to Diet, my chapter on fat-blocking foods starts out with a command to “Eat Your Thylakoids,” doctor’s orders. What the heck is a thylakoid? Just the source of nearly all known life and the oxygen we breathe. Thylakoids are where photosynthesis takes place––the process by which plants turn light into food. Thylakoids are the great green engine of life, microscopic sac-like structures composed of chlorophyll-rich membranes concentrated in the leaves of plants.
When we eat thylakoids––when we bite into a leaf of spinach, for instance––those green leaf membranes don’t immediately get digested. They can last for hours in our intestines, and that’s when they work their magic. Thylakoid membranes bind to lipase. Lipase is the enzyme our body uses to digest fat; so, if you bind the enzyme, you can slow fat absorption. It’s like a natural version of the fat-blocking drug orlistat, but without the anal leakage. This is because the effects of the thylakoids are temporary. Unlike the drug, the thylakoids do finally break down eventually, freeing the lipase enzyme to do its job before fat comes spilling out your other end. Ultimately, fat absorption is not so much blocked by thylakoids as it is delayed.
If all the fat is eventually absorbed, what’s the benefit? Location, location, location. There’s a phenomenon known as the ileal brake. The ileum is the last part of the small intestine before it empties into your colon. When undigested calories are detected that far down in our intestines, our body thinks we must be full from stem to stern, and puts the brakes on eating more by dialing down our appetite. This can be shown experimentally. If you insert a nine-foot tube down people’s throats and drip in any calories—fat, protein, or sugar—you can activate the ileal brake. Then, sit them down to an all-you-can-eat meal, and compared to the placebo group who had just gotten a squirt of water through the tube, they eat over 100 calories less. You just don’t feel as hungry. You feel just as full, eating significantly less. That’s the ileal brake in action.
So, with thylakoids delaying calorie absorption until that tail end of your small intestine, strong satiety signals are sent to the brain, which dials down your appetite. If you feed someone a meal with added thylakoids (by slipping in some powdered spinach), and measure the level of hormone release into their bloodstream over the next six hours, you see a significant rise in a satiety hormone called CCK, and a drop in the hunger hormone ghrelin. Does this then translate into a drop in appetite? Researchers were eager to find out.
Spinach extracts were disguised in jam or juice to sneak thylakoids into meals, and those unwittingly eating the equivalent of about a half cup of cooked spinach felt significantly less hungry and more satiated over the next few hours. Give someone the equivalent of a shot of wheatgrass juice in the morning, or what they might get in a “green drink” or green smoothie, and not only do they feel less hungry, more satiated, their cravings for presented salty, sweet, and fatty snacks (for example, potato chips, gummy bears, chocolate, and cinnamon buns) drop by about a third. Feed them candy anyway, and those who unknowingly had been snuck some spinach report liking the sweets significantly less. The satiating power of greens has been attributed to their high water and fiber content and low-calorie density, but the thylakoids may be their secret weapon.
Most thylakoid trials have shown improved satiety, but the real test is weight loss. Researchers in Sweden randomized overweight women to blended blueberry drinks every morning with or without “green-plant membranes” (in other words, just covertly slipping them some powdered spinach), and they get a boost in appetite-suppressing hormones, and a decreased urge for sweets. Yes indeed, spinach can cut your urge for chocolate. Check this out: seven hours after eating spinach, you’re like, chocolate? Eh. Got any more spinach? And…boom, accelerated weight loss, all thanks to eating green—the actual green itself—the chlorophyll-packed membranes in the leaves.
Within 12 weeks, the women who were slipped spinach lost 11 pounds––significantly more than the control group. And, as a bonus, their LDL cholesterol dropped too, even before the weight loss started kicking in. If you instead fix their calorie intake to force the same weight loss, those randomized to the spinach group may have had an easier time with eating less––experiencing less hunger after a test meal after weeks eating green.
Extracts of spinach were used in these studies so they could create convincing placebos, but you can get just as many thylakoids eating about a half cup of cooked greens, which is what I recommend people eat at least two times a day in my Daily Dozen checklist of all the healthiest of healthy things I encourage people to try to fit into their daily routine.
Which greens have the most? You can tell just by looking at them. Because thylakoids are where the chlorophyll is, the greener the leaves, the more potent the effect. So go for the darkest green greens you can find, which in my area is the lacinato or dinosaur kale.
What happens when you cook greens? Blanched for 15 seconds or so in steaming or boiling water, they actually get brighter green. But then if you cook them too long, they eventually turn a drab olive brown. When you overcook greens, the thylakoids physically degrade, along with their ability to inhibit lipase. But within that first minute or so, when the green gets even more vibrant, there’s a slight boost in fat-blocking ability. So, you can gauge thylakoid activity in both the grocery store and the kitchen with your own two eyes.
The best green vegetable, though, and the best way to cook it, is whichever and however you’ll end up eating the most. We have been chewing on leaves for millions of years, but today the greenest thing about some people’s diets may be a St. Patty’s Day pint. Americans have averaged less than two grams of spinach a day, less than half a teaspoon. Your body was designed to have thylakoids passing through your system on a daily basis; so, the delay in fat absorption can be thought of as the default, normal state. It’s only when we eat greens-deficient diets that the accelerated fat digestion undercuts our natural satiety mechanisms. In the Journal of the Society of Chemical Industry, a group of food technologists argued that given their fat-blocking benefits, “thylakoid membranes could be incorporated in functional foods as a new promising appetite-reducing ingredient.” Or you can just get them the way Mother Nature intended.
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