I wish I had spent more time trying to understand Chemistry 101, instead of just worrying about flunking out of that freshman class. Because as the debate rages on about which diet is better for you: Paleo, Keto, Vegan or Mediterranean, there is one inarguable fact: Food is chemistry. And how it affects our bodies starts moments after we eat. When those molecules reach the intestines they turn on and off the bacteria growing in our gut, which in turn determines our future heart health, cellular function, and day-to-day energy level.

It turns out that diet is as important as genes in determining your overall health, and you can change your gut bacteria for the better in as little as just four days! That's all it takes, says one leading expert I interviewed recently. We all know diet had long-term effects on our health, but it also can have a quick impact, and it all starts with the balance of what happens in your gut.

We hear a lot about the "microbiome," which is basically a fancy word for the bacterial growth and environment in our intestines, and whether the bacteria that grow there is "good bacteria" that promote healthy cellular function or "bad bacteria" that can lead to heart disease and other ailments. The bacteria that grows is determined by what we eat.

Your gut bacteria send out signals (chemical compounds) via the bloodstream to tell your body to either brace itself for incoming fat and animal protein or get soothed and sustained by plant fiber, antioxidants, and other natural nutrients that grow in the ground.

Faecalibacterium prausnitzii bacteria, illustration
Getty Images

Never a chemistry or biology jock, I need to let the experts explain how this works: For that, I went to visit Dr. Hooman Yaghoobsadeh, a well-known cardiologist at New York Hospital, who is also on the faculty at Weill Cornell Medical School. He also happens to be my doctor, and also just coincidentally espouses a plant-based diet for long-term (and short-term) health.

When I told Dr.Yaghoobsadeh that I had gone plant-based a year after first meeting him he got so excited that he invited me up to his office for a 45-minute lecture that he gives to medical students and others around the country, to show how a plant-based diet works to reverse heart disease and stave it off in those who are still symptom-free. (Other cardiologists have since told me that if we are over the age of 18 and eat a traditional meat-and-dairy-laden American diet, we all have heart disease, it's just that half of us don't know it yet.) I arrive at Dr. Yaghoobsadeh's office and am immediately given a lecture that takes me back to my Intro to Chem days, though this time I  pay rapt attention, and this time, I understand what's at stake.

Dr. Yaghoobsadeh

Let's start with a few key facts (get ready to pay attention since there are some freaky factoids here, which would have kept me from failing Chem if this had been part of the lecture). Such as the fact that there are more than 2 million bacteria-owned genes in your gut, more even than the number of genes in the human cells that make up your body. And these bacteria genes impact your health as much as the genes you were born with.

1. There's more DNA that is bacteria in your body than in your human cellular self.

In your gut, you have 300 to 500 bacterial species, which together represent 2 million genes—which make up your microbiome. So the DNA of the bacteria in your gut is approximately 10 times that of all of the cells in your body. The collective bacterial genome is like the Milky Way galaxy, compared to the Solar System of our human genome.

2. We are what we eat. And we can change that for the better. It happens quickly.

That means that when you change what you eat, you literally change what and who you are. We can change who we are in just six weeks. In fact, it starts to happen in just four days.

The microbiome and us humans co-evolved over 200 million years, but only in the last minute -- actually a few hundred years--have we increased the amount of meat we eat to outpace the plant foods and fiber we eat. And when you go off that animal product, it takes a handful of days to alter your gut bacteria and switch over from meat-metabolizing to plant-metabolizing, and that changes the whole system. The dietary influence of your food choices is as important to your health than the DNA you got from mom and dad!

3. Fiber keeps blood sugar steady, insulin low, and body not to store calories as fat.

When you feed humans plants, their gut switches over from animal bacteria to plant bacteria and that triggers a cascade of signals in the body to keep blood sugar steady and insulin levels in check -- so your body is not instructed to cart off any extra calories to fat storage.

When you eat more fiber foods, your entire body reacts differently. Fiber-eating bacteria are programmed to metabolize the fiber in plants. It helps your food move through the body's digestive tract and your intestines without raising blood sugar and causing insulin to spike, which signals the body to store extra sugar as fat.

By eating more fiber in every meal, and keeping the carb-to-fiber ratio at less than 7, the lower the better, the more you keep blood sugar steady and insulin levels in check, all good if you're trying to maintain a healthy weight. So when you choose a protein bar or other packaged item, look for that ratio. If the carbs are 21 grams, then the fiber needs to be 3 or higher.

Fiber is the key to modern-day health, says Dr. Yaghoobzadeh. When you move away from animal products you make more room for fiber in your diet. Animal proteins go rancid—which is why the bacteria in your gut that feed on animal proteins are inflammatory.

Every major disease is linked to inflammation. Dr. Yaghoobsadeh calls it the first domino in most diseases. When that domino falls—meaning inflammation in the body spikes—it affects insulin, it can lead to heart disease, and it can lead to arthritis and slowness to recover from injury.

Or to quote Dr.Yaghoobsadeh, "A move to a plant-based diet leads to selection against proteolytic or protein eating bacteria and selection for fiber eating bacteria known as fermenters." So probiotics and fermentation are linked. The more you add fermented foods, the more you help all this healthy switch in your gut bacteria to a healthy balance.

4. Meat-eating metabolites tell blood vessels to constrict, harden, and clog with plaque.

When you eat animal products, the bacteria shift to protein-eating bacteria, and your system goes into overdrive to create metabolites that break down meat. Animal proteins are broken down in the gut with the metabolite TM, which your liver makes into TMAO. Too much TMAO leads to inflammation, hardening of the arteries and plaque that blocks blood flow.

People with high levels of TMAO in their bloodstream have twice the risk of heart disease and higher incidents of death from any cause, according to a study published by Harvard Women's Health Watch. TMAO leads to inflammation, changes the way your body deals with cholesterol and also leads to plaque building up in your blood vessels, Dr. Y explains. The more animal protein patients eat, the higher their lifetime risk of heart disease.

Inflammation is the first line of defense when your body is under siege. Your body's immune system is triggered not just by viruses but by the food you eat, and inflammation can result in symptoms as varied as arthritis, achy joints or puffiness, and bloat. It may not be the sodium in your BBQ, but the meat itself that gave you all those puffy or achy feelings the next day.

5. Bottom line: It only takes 4 days to shift from bad bacteria to good. And that is helpful!

The fewer animal product you eat, the healthier your gut balance will be. It only takes 4 days to shift the balance from bad bacteria to good bacteria, so if you eat meat, know that you can reverse all these processes in just half a week. It's that fast. And if you don't eat meat but you slip up, move on and get back on track, because a little bit of animal or dairy product is not enough to turn back on the bad bacteria. You have to do it repeatedly for days in order to have the gut switch back over to meat-eating bacteria.

Once you shift over to a mostly plant-based diet, the gut bacteria shifts over too, and the new fiber-eating bacteria can't select or break down the TMA, so it just slips past the whole process. Your metabolism shifts over after about six weeks to not be able to break it down. That means your system burns on healthy fiber-based foods, and the others just go unnoticed. Of course, if you begin to shift back to animal products consistently, your gut will readjust too, but the occasional spec of cheese, meat or dairy is not enough to trigger that.

6. How much protein do I need? Not as much as you may think:  About 50 to 65 grams.

If you are training for an event and trying to build muscle, you may need more than the average amount. But the usual recommended daily intake is .8 grams of protein per kilogram of body weight or 0.36 grams per pound. So a woman of 140 pounds needs 50 grams and a man who weighs 175 pounds needs about 603 grams a day. Add more if you're trying to get larger, or training for something like an ironman, and less if you'd like to lean down a bit.  Even if you're a jock, your body isn't sure what to do with more than 75 grams of protein a day. It just makes your gut go into overdrive, to figure out how to metabolize all that extra protein.

That means that if you tell yourself you're eating animal products for protein, you don't need to. For the best sources of plant-based proteins, including vegetables, fruits, nuts, seeds, and grains, check out The Beet's story on the top sources of protein. A bowl of oatmeal with almond or oat milk delivers 10 grams, and quinoa and lentil or chickpeas salad delivers another 20 grams for lunch. Snack on hummus, a handful of almonds or pumpkin seeds, then plan a stir fry and tofu over rice for dinner and you are good for the day. There is not much more to chemistry than that.

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