Vinegar Caveats

As I note in my chapter on greens in my book How Not to Die, vinegar may be one condiment that’s actually good for you. Randomized controlled trials involving both diabetic and non-diabetic individuals found that adding just two teaspoons of vinegar to a meal may improve blood sugar control, effectively blunting the blood sugar spike after a meal by about 20 percent. How? I discuss this in my video Vinegar Mechanisms and Side Effects.

Originally, we thought it was because vinegar delayed the gastric emptying rate, slowing the speed at which a meal leaves your stomach, which makes sense because there are acid receptors in the first part of the small intestine where the stomach acid is neutralized. So, if there is excess acid, the body slows down stomach emptying to give the intestine time to buffer it all. The acid in vinegar was thought to slow the rate at which food leaves the stomach, resulting in a blunted sugar spike. But then, studies were published where taking apple cider vinegar before bedtime resulted in lower blood sugars the next day. How does that work? That’s obviously not some acid-induced stomach-slowing effect. Indeed, anyone who actually went to the trouble of sticking an ultrasound probe on someone’s stomach could have told you that—no difference in stomach-emptying times was found comparing vinegar to neutralized vinegar. So, it’s not just an acid effect.

Back to square one.

Additional studies offered the next clue. Vinegar appeared to have no effect on blood sugars, but this was after giving people a straight glucose solution. Glucose is a byproduct of sugar and starch digestion, so if vinegar blunts the blood sugar spike from cotton candy and Wonder Bread but not glucose, maybe it works by suppressing the enzymes that digest sugars and starches. And, indeed, vinegar appears to block the enzyme that breaks down table sugar. It wasn’t just an acid effect, however. There appears to be something unique about acetic acid, the acid in vinegar. These findings were based on intestinal cells in a petri dish, though. What about in people? Feed people some mashed potatoes with or without vinegar, and glucose flows into the bloodstream at the same rate either way—so, there’s another theory shot down.

Let’s figure this out. If sugar enters the bloodstream at the same rate with or without vinegar, but vinegar leads to significantly less sugar in the blood, then logically it must be leaving the bloodstream faster. Indeed, vinegar ingestion appears to enhance sugar disposal by lowering insulin resistance (the cause of type 2 diabetes), and also appears to improve the action of insulin in diabetics. The mystery of how vinegar works appears to have been solved, at least in part.

So, diabetics can add vinegar to their mashed potatoes—or just not eat mashed potatoes. If you add vinegar to a high-fiber meal, nothing happens, which explains results such as no effects of vinegar in diabetics in response to a meal. That’s no surprise, because the meal in question in the study was mostly beans. If you are going to eat high glycemic index foods like refined grains, vinegar can help—though there are some caveats.

Don’t drink vinegar straight, as it may cause intractable hiccups and can burn your esophagus, as can apple cider vinegar tablets if they get lodged in your throat (not that apple cider vinegar tablets necessarily actually have any apple cider vinegar in them in the first place). Don’t pour it on your kid’s head to treat head lice either. It’s “not harmful except when it leaks on to the face or penetrates the eyes,” and it turns out it doesn’t even work. Vinegar can also cause third-degree burns if you soak a bandage with it and leave it on.

Though as many as a total of six tablespoons a day of vinegar was not associated with any side effects in the short-term, until we know more, we may want to stick with more common culinary type doses, like two tablespoons max a day. For example, drinking 2,000 cups of vinegar was found to be a bad idea.


Other good-for-you condiments include (salt-free) mustard and horseradish. You may be interested in my Second Strategy to Cooking Broccoli video. For more on my book, check out the trailer.

This is the final installment of my five-part series on vinegar. If you missed any, here they are:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Do Smoothies Cause Overly Rapid Sugar Absorption?

Drinking sugar water is bad for you, as I explored in If Fructose Is Bad, What About Fruit?. If you have people fast and then drink a glass of water with three tablespoons of sugar in it, which is about the amount in a can of soda, you get a big spike in blood sugar within the first hour. Our body freaks out and releases so much insulin that we actually overshoot. By the second hour, we’re relatively hypoglycemic, dropping our blood sugar below where it was when we started out fasting. In response, our body dumps fat into our bloodstream as if we’re starving because our blood sugars just dropped so low. The same thing happens even after drinking apple juice.

In the three hours after eating four and a half cups of apple slices, your blood sugar just goes up and comes down normally. (You can see all of these spikes and drops in my Green Smoothies: What Does the Science Say? video.) What happens if you take in the same amount of sugar in apple juice form—about two cups? Your body overreacts, releasing too much insulin, and you end up dipping below where you started. The removal of fiber in the production of fruit juice can enhance the insulin response and result in this “rebound hypoglycemia.”

What would happen, though, if you put those four and a half cups of sliced apples in a blender with some water and pureed them into an apple smoothie? Despite still having all the fiber, it still caused that hypoglycemic dip. The rebound fall in blood sugars, which occurred during the second and third hours after drinking juice and puree, “was in striking contrast to the practically steady level after eating apples.” This finding not only indicates how important the presence of fiber is, but also perhaps whether or not the fiber is physically disrupted, like in a blender.

Let’s play devil’s advocate. Eating four and a half cups of apples took 17 minutes, but drinking four and a half cups of apples in smoothie form only took about 6 minutes, and you can down two cups of juice in about 90 seconds. So, maybe these dramatic differences have more to do with how fast the fruit entered our system rather than its physical form. If it’s just the speed, we could simply sip the juice over 17 minutes and it should be the same, right? Researchers put it to the test. They found this had the same results as drinking quickly. So, it wasn’t the speed—it was the lack of fiber. What if you disrupt that fiber with blending but sip it as slowly as the apple eating? The results were a little better, but not as good as just eating the apple. The take-away? Eating apples is better than drinking apple smoothies, but who drinks apple smoothies? What about bananas, mangoes, or berries?

There was a study that compared whole bananas to blended bananas and didn’t see any difference, but they only looked for an hour and it was while participants were exercising. Bananas in general, though, may actually improve blood sugars over time. The same goes for mangoes, as demonstrated with powdered mango, and you can’t get any more fiber-disrupted than that. It may be due to a phytonutrient called mangiferin, which may slow sugar absorption through the intestinal wall.

Berries help control blood sugar so well they can counter the effects of sugar water even when they’re pureed in a blender. By adding blended berries to sugar water, you don’t get the hypoglycemic dip and you don’t get that burst of fat in the blood. Drinking blended berries isn’t just neutral—it improves blood sugar control. Again, this is thought to be due to special phytonutrients that may slow sugar uptake into the bloodstream. Indeed, six weeks of blueberry smoothie consumption may actually improve whole body insulin sensitivity.

So, while apple smoothies may be questionable, a recipe like The Mayo Clinic’s basic green smoothie recipe, which is packed with berries and greens, would be expected to deliver the best of both worlds—maximum nutrient absorption without risking overly rapid sugar absorption.


I have a whole series of videos on green smoothies. In Are Green Smoothies Good for You?, I talk about the enhanced nutrient availability absorption. In Are Green Smoothies Bad for You?, I raise the questions about teary-eyed gut flora and intact grains, beans, and nuts. For even more, see Liquid Calories: Do Smoothies Lead to Weight Gain? and The Downside of Green Smoothies.

Is there any limit to whole fruit? See How Much Fruit Is Too Much?.

What about fructose? Is it bad? Watch my videos Apple Juice May Be Worse Than Sugar Water, How Much Added Sugar Is Too Much?, and Big Sugar Takes on the World Health Organization.

Since digesting food creates free radicals, we need to be sure the food we eat is packed with antioxidants. See Minimum “Recommended Daily Allowance” of Antioxidants, How to Reach the Antioxidant “RDA”, and Antioxidant Rich Foods with Every Meal.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Why Intact Grains are Even Better than Whole Grains

Fruits and vegetables are the most nutrient-dense foods on the planet, and dark green leafy vegetables lead the pack. Each of the top five so-called powerhouse fruits and vegetables were greens. If we blend them up in a smoothie (or soup or sauce), we’re taking the food with the most nutrition and breaking all the cells to dump that nutrition into our bloodstream. Chewing is good, but blending is better in terms of digestive efficiency and nutrient absorption.

But if we take in all that nutrition and none makes it down to our colon might we be starving our microbial selves? The reason intact grains, beans, and nuts are better than bread, hummus, and nut butters is that no matter how well we chew, intact food particles make it down to your colon where they can offer a smorgasbord for our good bacteria. If our grains, beans, and nuts are finely ground up into flour or paste before we eat it, we may be leaving our gut flora high and dry. Would the same be true for fruits and vegetables?

There are special classes of phytonutrients in fruits and vegetables that appear to protect against colon cancer. They can escape digestion and absorption in our stomach and small intestine, and end up in our colon to act as prebiotics. No matter how much we chew, they stay attached to the fiber. But if we use a blender, might we prematurely detach these nutrients? No. Even if you blend in a high-speed blender for five minutes, the phytonutrients remain bound to the fiber for transport down to your colon bacteria. You can do smoothie experiments on people with ileostomy bags that drain the contents of the small intestine and show that most of the polyphenol phytonutrients make it out intact, so we don’t have to worry we may be robbing Peter to pay Paul when we blend fruits and vegetables. Is there any downside to smoothies, then?

Just as smaller particle size may improve digestive efficiency and gastrointestinal absorption of nutrients from fruits and vegetables, the same may be true for grains. There is, however, a concern that this could boost starch availability and cause a blood sugar spike. In my video Are Green Smoothies Bad for You?, I show you the rise and fall of blood sugar and insulin over four hours after eating a half-cup of brown rice compared with ground brown rice flour (kind of like a cream of brown rice hot cereal). Consuming brown rice flour gives you twice the blood sugar and twice the insulin spike compared to eating the rice intact. Same amount of food, just in a different form. This is why intact whole grains are better than even whole grain flour products.

Simply chewing really well can boost the glycemic and insulin response. If you chew rice really well compared to chewing it normally, the smaller rice particles empty out of your stomach faster, producing greater blood sugar and insulin responses. It’s ironic that there were health crusaders pushing people to chew more to digest their food better, but if what you’re chewing is a five cheese pizza, maybe it’s better not to digest so well. Believe it or not, some have even suggested that diabetics and obese persons should not chew their food so much. But, swallowing diced food without chewing would not only reduce the pleasure of eating—people could choke! Despite this, they suggest it could be a simple way to “allow patients to reduce blood glucose [sugar] levels without fundamentally altering their diets and may thus prove more acceptable” than having to do the unthinkable—just eat high fiber foods like beans, which have been shown to blunt blood sugar spikes.

What about blended beans like hummus? Unlike grains, blending legumes doesn’t affect their glycemic response. So, let’s circle back to the smoothie question: Is fruit more like grains or more like beans? If you liquefy fruit in a blender to make a smoothie, do you risk spiking your blood sugar too high? To find out, watch my Green Smoothies: What Does the Science Say? video.


My general take on beans is simple: the more beans, the better—however you get them. For more information, watch my videos Beans and the Second Meal Effect, The Hispanic Paradox: Why Do Latinos Live Longer?, and Canned Beans or Cooked Beans?.

Want more on smoothies? Here it is:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: