If you have a long-standing weight problem, you’ve almost certainly experienced this: The more you diet, the harder it is to lose weight. For years scientists attributed this to a change in metabolism but had no real explanation for the mechanism. Now researchers at the Weitzman Institute in Israel have discovered a compelling explanation. Their research was done in mice, but it’s readily translated to humans and, most importantly, it points to a simple dietary treatment. The research deals with one of the most important topics in nutritional medicine today, the interaction between bacteria in your gut (the gut microbiome) and phytonutrients called flavonoids found in the food you eat.
Flavonoids are polyphenols, chemicals naturally produced by plants. There are over 400 flavonoids in the human diet, and the average Western diet supplies about 1,000 milligrams a day. Asian diets supply four to five times that amount, mostly from teas and spices. Best known for their anti-inflammatory and anti-cancer effects, flavonoids can influence almost every system in your body. High intake of flavonoids in the diet has been associated with decreased risk of many chronic diseases and allergies.
The flavonoid-gut bacteria connection you should know about.
Dietary flavonoids have a complex relationship with gut bacteria. Bacteria can liberate flavonoids from the food you eat, increasing their absorption, or they may destroy those flavonoids. Flavonoids, for their part, shape the distribution of gut bacteria; they alter the gut microbiome, increasing its internal diversity, which is generally considered a good thing.
The scientists at the Weitzman Institute did not start out looking at flavonoids. They wanted to study the impact of yo-yo dieting on the gut microbiome. There are two ways to study the microbiome, and these scientists looked at the impact of yo-yo dieting in both ways. The first approach answers the question, "Who’s there?" (What bacterial species are present?) There are about a thousand species found normally, and many more if strains and subspecies are studied. The second approach answers the question, "What do they do?" Different bacteria may affect your body in exactly the same way; conversely, different strains of the same species may have drastically different effects.
Yo-yo dieting and its effect on gut health.
To produce yo-yo dieting in mice, the Weitzman researchers first fed them a diet of standard laboratory chow. For mice, this is a vegetarian low-fat diet. Then they started loading the mice up with fat, which made them gain weight. Next, they returned them to standard lab chow with restricted calories, so that they lost weight, and then they kept repeating the cycle of weight gain and weight loss over and over.
What they found will be no surprise to dieters. Each time the overfed mice lost weight, it became easier for them to regain it and harder for them to lose it again. Each cycle of weight loss and weight gain increased this effect. When they studied the gut microbes of the dieting mice, they found an explanation. On the high-fat diet, the mice experienced a loss of diversity among their gut bacteria. When they lost the weight, diversity increased but never returned to where it had been before the weight gain. With each episode of weight gain, the disturbance in gut microbes was greater, and each subsequent round of weight loss was less effective at restoring a normal balance to the gut microbiome. This part of the research was answering the question, "Who’s there?"
The critical effect of dieting became obvious with the answer to the second question, "What do they do?" That finding is a real breakthrough in understanding how disturbed gut bacteria cause weight gain. The altered gut bacteria became more efficient at destroying flavonoids. The more cycles of weight gain and loss the mice experienced, the greater the capacity of their gut microbes to destroy flavonoids, so flavonoid levels in the blood of these mice dropped dramatically over time.
Drawing connections between flavonoids, bacteria, and weight management.
Here’s what’s remarkable about this finding: If you feed bacteria a particular nutrient, they’re likely to increase their ability to metabolize that nutrient. But the high-fat weight-gain diet is actually much lower in flavonoids than standard lab chow. So the increased ability of these bacteria to destroy flavonoids was not simply the result of feeding the mice more flavonoids. It paradoxically occurred when they were consuming fewer flavonoids, indicating that this change reflects a deep-seated alteration in the function of the gut microbiome—not just a reversible effect induced by a short-term feeding practice.
So what's the solution? There were two specific flavonoids that were especially depleted after rounds of yo-yo dieting: apigenin and naringenin. Each of these has profound effects in humans. Apigenin has anti-inflammatory and anti-allergic effects and alters the metabolism of fat cells. Naringenin is a powerful antioxidant with anti-inflammatory effects and plays a profound role in detoxification. The Weitzman researchers noted that both flavonoids increase metabolic rate and suppress appetite. When they fed supplements of apigenin and naringenin, their obese yo-yo dieting mice began to lose weight like normal mice. Feeding these flavonoids overcame the effects of yo-yo dieting.
The good news about apigenin is that it’s concentrated in parsley and celery leaves. Naringenin is a citrus bioflavonoid, most concentrated in grapefruit. You don’t need supplements to duplicate the Weitzman effect. You only need the right foods. Parsley, grapefruit juice and celery (include the leaves) make a tangy and refreshing drink.
If you drink celery juice every day for a month will it heal your gut? Find out here.
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