Research Roundup

You know the feeling you get – when you learn something new about a health problem you’ve been trying to reverse – maybe high blood pressure, diabetes, or heart disease. Well – there’s nothing I like better than bringing you the information that will help you do just that. Welcome to the NutritionFacts podcast. I’m your host – Dr. Michael Greger.

Today, we begin a new series with the latest research on a variety of topics.  And first up – we look at the benefits of vinegar for blood sugar control and polycystic ovary treatment.

The use of vinegar for weight loss dates back to the 1700s. I did a whole chapter about it in my book How Not to Diet entitled “Amping AMPK,” the fat-controller enzyme in the body, which appears to be the mechanism behind the multitude of beneficial metabolic effects. In my 21 tweaks to accelerate weight loss, I recommend two teaspoons with every meal, which is considered safe––though it should be added to food or diluted in water, never consumed straight. And diabetics should make sure the vinegar doesn’t make their blood sugars go too low.

But that’s one of the benefits of vinegar: blunting the blood sugar and insulin spikes after a meal in both healthy individuals and those with blood sugar disorders like diabetes. In a systematic review and meta-analysis of interventional trials on the effects of vinegar consumption on blood sugar control in type 2 diabetes, vinegar improves both short-term and longer-term measures of blood sugar control. And, as a little side bonus, it resulted in a remarkable reduction in cholesterol to boot. And it didn’t seem to matter whether it was apple cider vinegar or not. All vinegar, by definition, has the active ingredient: acetic acid.

So, what are the implications for clinical practice? Well, clinicians could incorporate vinegar consumption as part of their dietary advice for patients with diabetes, with the caution that it can work a little too good. So, you have to monitor closely to make sure diabetic patients aren’t overmedicated and bottom out their sugars.

In my video on water purification, I talked about a study showing that the cheapest and best way to disinfect your toothbrush so you don’t have to keep buying new ones may be to soak it for 10 minutes in 50 percent white vinegar in water.

So, what about a vinegar sock soak for athlete’s foot or toenail fungus? Foot soaks in half vinegar/half water can help antifungals work better, but the inconvenience of tub soaks limits compliance. So, how about pouring vinegar and water on the toes of your socks, and then just putting your feet up for a little while? Not sure how that would be any more convenient, but it seemed to work in this clinician’s practice.

Instead of vinegar for just an athlete’s foot, what about vinegar for the whole athlete? “The Effect of Vinegar Supplementation on High-Intensity Cycling Performance.” They randomized people to do two tablespoons of diluted vinegar, or sugar, or both, or neither, and…the vinegar did nothing. Is there anything else vinegar does help with?

Another study: “Intake of Vinegar Beverage Is Associated with Restoration of Ovulatory Function in Women with Polycystic Ovary Syndrome.” For those of you not familiar, polycystic ovary syndrome (PCOS) is a major cause of irregular menstruation. And since insulin resistance has been suggested to be one of the causes of polycystic ovaries, and we know vinegar can improve insulin resistance, researchers decided to study the effect of vinegar by giving seven patients seeking a non-pharmacological treatment for PCOS a beverage containing a tablespoon of apple vinegar daily for a few months. The insulin resistance did improve in most, but did their cycles return?

Yes, in four out of seven. Before the study, they were either only having their periods every 50 days or so, or none at all, or just not ovulating. But most resumed within 40 days on the vinegar. Now, this doesn’t prove anything, but it’s at least sufficient to indicate the possibility that it may help. And what’s the downside? A tablespoon of vinegar would cost less than 10 cents a day. Just remember to never drink vinegar straight, as it can cause second-degree caustic burns down your throat.

Next up – we discover how coffee and tea may impair iron absorption, which may help explain some of their benefits.

In my videos on tea, I caution not to drink with meals, because it can inhibit the absorption of iron from foods anywhere from 26 to 99 percent, perhaps depending on the brewing time, brand, or how strong it is. What about the inhibition of food iron absorption by coffee?

When I was first looking this up, I ran across this study on the effects of discontinuing coffee intake on the iron status of Guatemalan toddlers. I’m thinking they must be talking about breastfeeding mothers or something, but no, coffee is one of the first liquids given to infants in Guatemala. I did not know that!

Anyway, the inhibition of food iron absorption by coffee. A cup of coffee reduced iron absorption from a hamburger meal by 39 percent, as opposed to a 64 percent decrease with tea. So, not as bad as tea, but still significant blockage. And just like with the tea, the stronger the coffee, the more iron absorption was impeded. In terms of timing, no decrease in iron absorption occurred when coffee was consumed an hour before a meal, but waiting an hour after the meal to drink the coffee didn’t seem to help. This can be probably explained by the fact that it may take up to nearly two hours to clear a meal from the stomach; so, starting an hour in, the coffee can catch up to the food.

Now, you can reverse the effect of tea or coffee by adding orange juice to a meal, or even better an orange, or any source of vitamin C-rich food. The vitamin C boosts iron absorption, which is good for people who are borderline anemic, but for many, the blockage of iron absorption from coffee may actually be a good thing.

Iron is a double-edged sword. On the one hand, iron is an essential element vital for blood production. On the other hand, iron is a potent pro-oxidant. So, maybe the reduced risk of type 2 diabetes associated with coffee consumption is due to the inhibition of iron absorption by coffee.

See, the risk of type 2 diabetes increases with the increase in the amount of ferritin in your blood, which is a measure of your iron stores. So, higher iron stores, higher diabetes risk. It’s the same thing with the risk of gestational diabetes during pregnancy. So, you need to make sure you’re getting enough iron, but not building up too much iron in your body. How do we know it’s cause and effect?

Because if you randomize diabetics to something like old-fashioned bloodletting, but instead of leeches, they just donate blood a couple times to lower their iron stores, and those in the blood donation group had better blood sugar control, better insulin secretion, and less insulin resistance. Iron depletion improves artery dysfunction in type 2 diabetics as well.

Same thing with gout. Does inhibition of iron absorption by coffee reduce the risk of gout? Let’s find out. Near-iron deficiency-induced remission of gouty arthritis. They took gout patients and maintained their iron stores at the lowest level possible without causing anemia and…gouty attacks markedly diminished in every patient, with effects ranging from a complete remission to a marked reduction of incidence and severity of gouty attacks. So, maybe that’s one reason coffee consumption is associated with lower risk of gout. It blocks some of the iron uptake.

Increasing evidence suggests that iron is also involved in multiple diseases of aging, including Alzheimer’s disease, Parkinson’s disease, and heart disease. In terms of iron and Alzheimer’s, they think it’s iron’s potential to effectively “rust” brain tissue by producing free radicals that may cause neurodegeneration, contributing to Alzheimer’s disease pathology at numerous levels––so much so that there is interest in trying to treat Alzheimer’s disease by targeting iron.

High body iron stores may also be associated with shorter telomeres, which is a biomarker of biological aging. And for those of you thinking, well if I had high iron stores, I’d probably know about it. But only 5 percent of patients with elevated iron report ever being told by a doctor that this was the case.

To prevent too much iron accumulation, regularly drinking tea with meals will do it, found to decrease the amount of bloodletting you have to do for people with a genetic iron overload disease. But you’d want to do the opposite—drink tea only apart from meals—if you were at risk for iron deficiency anemia.

Besides tea and coffee, there are other beverages that can block iron absorption. Peppermint is right up there with black tea. Chocolate milk would do it too. And chamomile blocks iron about in the same range as coffee. So, if your iron stores are high, these are great mealtime choices. If you’re struggling to get enough iron, you wouldn’t want to regularly drink these with meals.

We think it’s the polyphenol phytonutrients. So, what about herbs and spices? They’re packed with polyphenol goodness.

Now, this study was done basically in a test tube, not in real people, but there is this case report of iron deficiency anemia due to high-dose turmeric. A physician treated himself for an osteoarthritis flare with capsules of turmeric extract, and he was anemic, couldn’t get his iron up despite taking iron supplements. But two weeks after stopping the turmeric, his blood count and iron levels were all back to normal.

So, on one hand, those presenting to doctor’s offices with iron deficiency anemia should be asked about supplement use; at the same time, the ability of turmeric to glom on to intestinal iron may lead to it being useful in states of iron overload.

Finally today – we look at how a single meal high in saturated fat can impair cognition.

Having a high cholesterol level in your early 40s is associated with an increased risk of Alzheimer’s and vascular dementia decades later. And your cholesterol doesn’t have to be that high to increase dementia risk. A 57 percent higher risk of developing Alzheimer’s at a total cholesterol of 240 compared to under 200. I’ve done a bunch of videos talking about the clogging of the cerebral arteries inside of the brain with the same atherosclerosis that causes heart attacks and strokes, choking off blood flow to the memory centers in the brain.

This may be why higher saturated fat intake was found to be associated with the development of worse global cognitive function and memory decline, an apparent acceleration of brain aging as if you were six years older. How can we cut down on saturated fat? By cutting down on cheese, cake, ice cream, and chicken––essentially the top sources in the American diet, but also pork, burgers, and beef in general.

In my video on the role of glycotoxins in cognitive decline, I profiled this study, showing that just five days of a high-fat, low-carb diet impairs energy metabolism in the heart, as well as cognitive function, concluding such diets are detrimental to the heart and brain. Now, they were thinking the impaired energy production may have accounted for the brain dysfunction as well, but high levels of dietary glycotoxins, so-called AGEs, are also associated with cognitive decline. So, we may want to cut down our intake of baked, broiled, or grilled meat, chicken, or fish, as well as certain dairy products. But there’s another possibility.

“Metabolic Endotoxemia: A Potential Underlying Mechanism of the Relationship between Dietary Fat Intake and Risk of Cognitive Impairment.” Endotoxins are highly pro-inflammatory components of certain types of bacteria, like E. coli, that are released when bacteria die. They can end up being absorbed through our gut wall and end up in the bloodstream, resulting in what’s called endotoxemia. The highest levels of these endotoxins are found, not surprisingly, in foods like meat that are contaminated with bacteria––both red meat and white meat. And having elevated levels of endotoxins circulating in your bloodstream may be detrimental for healthy aging––associated with a large range of diseases, such as obesity, type 2 diabetes, heart disease, and depression.

Put people on a high-fat, low-carb diet for five days, and endotoxin levels in the bloodstream roughly double. Endotoxin levels before and after a few days on a high-fat diet. In fact, even a single meal can do it. Give people some sausage and egg McMuffins with hash browns, and you can get a significant increase within hours after the meal. How do we know it wasn’t the refined carbs in the muffin or something? Because the control meal had a muffin too, but lower fat and no sausage and egg. In fact, you can have people chug straight sugar water, and no change in endotoxin levels, whereas there was a big jump within hours drinking straight cream, which is pretty much straight fat. And not just any kind of fat, but mostly saturated fat.

A double-blind, randomized crossover trial demonstrated that a single meal high in saturated fat can impede attention (meaning the cognitive ability to distinguish target stimuli from distractors in a computer game), compared with an identical meal high in the kind of fat found more in nuts, seeds, and avocados. And this cognitive deficit was present five hours after the meal, and who knows how much longer after that.

There are two ways to cut down on endotoxin bursts after meals. One is to not eat so many in the first place. But if you do eat meat and dairy, the addition of fiber-rich foods can blunt the endotoxin surge. The same sausage and egg McMuffin endotoxin bomb, but with or without Fiber One cereal, which would be like 30 grams of fiber, and it seemed to glom on to the endotoxins, preventing the bump of endotoxemia three hours after the meal. The fiber also reduced the oxidative stress, the free radicals generated by such a meal––showing clearly that the addition of fiber to the high-fat, high-calorie meal had profound effects on metabolic and inflammatory events after the meal. And over time, meal after meal, this could have long-term implications.

Recent investigations reported higher abundance of endotoxins in the brains of patients with Alzheimer’s disease on autopsy—endotoxins building up in the memory center of the brain, the region of the brain that develops the earliest and most profound neuropathology in Alzheimer’s. Some advanced Alzheimer’s patients had up to a 26-fold increase in endotoxin levels over age-matched controls without dementia. And where were the endotoxins concentrated? Smack dab in the middle of the amyloid plaques, a pathology characteristic of Alzheimer’s.

For these and other reasons, proper nutrition has been proposed as a promising non-medical strategy to prevent cognitive decline and subsequent dementia.

We would love it if you could share with us your stories about reinventing your health through evidence-based nutrition. Go to nutritionfacts.org/testimonials. We may share it on our social media to help inspire others.  To see any graphs, charts, graphics, images, or studies mentioned here, please go to the NutritionFacts podcast landing page. There, you’ll find all the detailed information you need, plus links to all of the sources we cite for each of these topics. 

My last two books are “How to Survive a Pandemic” and the “How Not to Diet Cookbook.” Stay tuned for Dec 5, 2023 for the launch of my one “How Not to Age.” And – of course – all the proceeds I receive from the sales of all my books go to charity. 

NutritionFacts.org is a non-profit, science-based public service where you can sign up for free daily updates – or the latest in nutrition research via bite-sized videos and articles. Everything on the website is free. There are no ads, no corporate sponsorship, no kickbacks. It’s strictly non-commercial. I’m not selling anything. I just put it up as a public service, as a labor of love, as a tribute to my grandmother, whose own life was saved with evidence-based nutrition.