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Quick Summary tl;dr
Vinegar is a condiment you can feel good about including in your keto diet.
It adds flavor and "zing" to dishes, with almost no carbs (except for balsamic).
Plus, it's good for digestion, might help lower blood glucose and insulin after meals, and can even slightly decrease an elevated fasting glucose in people with dawn phenomenon.
Several of the most popular condiments have something surprising in common. Ketchup, mustard, mayonnaise, salsa, Worcestershire sauce, hot sauce, sriracha, and most store-bought salad dressings have very different flavor and texture profiles: some are sweet, some are salty and savory; some are watery and thin, others are oily and thick. Despite their diverse flavors and wide range of foundational ingredients, one thing unites these seemingly unrelated items: vinegar.
It’s true: I challenge you to go to a grocery store and take a good look at the condiments. You will see vinegar listed among the ingredients in almost all of them, and that’s not even taking into account the myriad forms of vinegar itself, such as apple cider vinegar, balsamic, red wine, champagne, sherry vinegar, and of course, no proper fish & chips meal would be complete without a generous splash of malt vinegar.
It’s also interesting to note that culinary traditions all around the world include various types of pickled vegetables or condiments. In East Asia, there’s kimchi and pickled ginger. In South America, they enjoy curtido; in Eastern Europe there’s sauerkraut and pickled beets, and proper French charcuterie plates and Italian antipasto trays typically include cornichons or brined olives, respectively.
Vinegar has been part of traditional ethnic cuisines around the world for centuries. And while we can’t assume that an ingredient or culinary technique is beneficial merely because it’s been employed by many disparate groups for a very long time, we ought to at least give that possibility some consideration. If certain culinary and gastronomic approaches have persisted through the ages, there are probably some good reasons why. Modern science is catching up to what the cooks of yesteryear seemed to know instinctively: vinegar has some interesting properties, some of which might be of special interest to people following a ketogenic or low-carb diet to help manage blood sugar.
Vinegar as a Natural Digestive Aid
As I mentioned, cuisines all over the world include some type of vinegar or pickled foods with meals. Is the bright tang vinegar provides the only reason for this, or did those ancient cooks know that vinegar brings something to food besides a pleasant little jolt to the tongue?
It’s not hard to connect the dots between vinegar and better digestion. After all, vinegar is acetic acid (molecular formula CH3COOH). As I discussed in my article on GERD and acid reflux, contrary to popular belief, for many people, indigestion and acid reflux result from too little stomach acid, rather than too much.
Hundreds of years ago, long before anyone had ever heard of HCl (stomach acid), it probably wasn’t difficult to observe that when acidic foods or condiments were consumed, digestion went a little more smoothly. (Especially back in the days before Facebook and smartphones, when there wasn’t a whole lot to do after a big meal except sit around and think about how your stomach was feeling.)
Pickling foods in vinegar is a very effective food preservation technique. Even foods that are naturally fermented will eventually end up pickled. Take wine, for example: grape juice is fermented into alcohol, but if the fermentation continues for a longer period of time, the end result is vinegar. In fact, this is where the word “vinegar” comes from: vin aigre, or “sour wine.” ( 1)
Vinegar is a Powerful Antimicrobial Agent
Vinegar is used as a food preservative precisely because it’s antimicrobial and deters against the proliferation of harmful bacteria. ( 2) For this reason, it’s also a go-to ingredient for non-toxic household cleaning applications, including laundry, wiping down countertops, and even cleaning windows. It was also used medicinally in wound care and fighting infections as far back as 2000 years ago. ( 3)
As an interesting aside, here’s a neat bit of information you can use at your next potluck gathering: surely you’ve heard tales of food poisoning caused by potato salad left out on a hot day, like at a summer picnic. Mayonnaise typically gets the blame for this, but guess what? It’s not the mayonnaise that goes bad; it’s the potatoes! It’s true! Mayonnaise contains enough vinegar to keep the bad bugs from proliferating in it. The potatoes, on the other hand, are a bacterial amusement park.
Vinegar Helps Moderate Blood Sugar
This is the most intriguing aspect of vinegar for people on low carb or ketogenic diets, especially for those eating this way to help manage type 2 diabetes or insulin resistance. A surprising amount of scientific literature confirms that vinegar has some impressive effects when it comes to moderating postprandial (after meal) glucose and insulin levels. Vinegar? For blood sugar regulation? Who would’ve thought?
Vinegar Reduces Postprandial Blood Glucose & Insulin
Here’s the overall gist:
In type-1 diabetics, type-2 diabetics, and healthy, non-diabetic subjects, vinegar reduces postprandial blood glucose and, to a lesser extent, postprandial insulin levels.
Taken collectively, studies examining the effects of vinegar on glucose and insulin have included subjects who use no medication as well as some on exogenous insulin and/or oral glucose control aids; people ages 21-79; and with BMIs ranging from approximately 21-34. (According to the BMI scale, a “normal” weight is a BMI of 18.5-24.9, overweight is classified as a BMI 25-29.9, and a BMI equal to or greater than 30 is considered obese.) (4) So the relevant studies encompass wide ranges of ages, body sizes, and medication status, which is important because it tells us the effects observed weren’t limited to healthy, lean, young people.
Taken as a whole, research indicates that vinegar reduces just about everyone’s blood glucose and insulin, but people with type 2 diabetes generally experience a less pronounced effect. (Meaning, their postprandial blood glucose is lower with vinegar than without it, but the reduction typically isn’t as large as that seen in non-diabetic subjects.) This may be because diabetics have poorer glucose control to begin with, so something that’s known to help will still help, but to a lesser degree than for someone who does not have diabetes.
A splash of vinegar isn’t powerful enough to get anyone off their medication, but considering the devastating effects of chronic hyperglycemia and hyperinsulinemia, it certainly never hurts for a diabetic to have another tool in their arsenal—particularly when it’s something as readily available and inexpensive as vinegar.
A Closer Look at the Science of Vinegar and Blood Sugar
Composition of the Meal Containing Vinegar
The effect of vinegar on blood glucose is different depending on the composition of the meal consumed. One study showed that vinegar was more effective in lowering postprandial glucose after a high-glycemic index (GI) meal versus one with a low GI. ( 5) This is probably because a meal with a lower GI would theoretically have less of an impact on blood glucose in the first place, so there’s less of an effect to be had anyway. The study involved type 2 diabetics (non-insulin dependent using diet or metformin alone for disease management), and demonstrated that 20 grams of wine vinegar (6% acidity) reduced postprandial glucose after a high-glycemic meal but less so after a low-glycemic meal containing the same total amount of carbohydrates and also matched for the same number of calories (isocaloric).
For a quick lesson into how mindboggling nutrition research is sometimes, the “low GI” meal in this study consisted of whole grain bread, lettuce, and low-fat cheese. Yes, bread. And low-fat cheese. Whole grain bread, yes, but still — bread, in a meal that’s supposed to be low glycemic. (I suppose it was, at least compared to the high GI meal, which was instant mashed potatoes and low-fat milk!) Anyway, according to the paper, the two meals contained the same amount of total carbohydrate, but the high glycemic meal had a GI of 86, compared to 38 for the low glycemic meal. ( 6) (The glycemic loads were 44 and 20, for the high and low meals, respectively. See here for more on the distinction between glycemic index and glycemic load.)
Composition of the Carbohydrates in a Meal Containing Vinegar
Related to the glycemic index of a meal, another factor that may influence the effect of vinegar on postprandial glucose (PPG) is the composition of the carbohydrates. A study looking at the effect of vinegar on PPG divided subjects into four randomized crossover intervention groups in which some subjects consumed a mix of simple and complex carbs while others consumed only simple sugars, in the form of a dextrose solution. ( 7) Three of the four study arms included healthy adults while the fourth included type 2 diabetics not on insulin. The study used both apple cider and raspberry vinegars, helping to establish that the glucose-moderating effects were not limited to apple cider vinegar, which is the one most commonly used in similar studies. Compared to placebo, 10 grams of vinegar (5% acidity) reduced PPG by 23-28% in healthy non-diabetic subjects consuming the starch and juice. In the diabetic subjects, the vinegar treatment resulted in a 13-17% reduction in PPG compared to placebo: less of a decrease than for the healthy subjects, but still potentially significant given the severe consequences of chronic hyperglycemia.
How did the study authors create a placebo for vinegar? Good question! (I mean, if you think about it, it should be pretty obvious when you’re eating or drinking something that has vinegar in compared to something that doesn’t.) One of the studies that used a placebo added saccharine (an artificial sweetener) to the vinegar to take away the acidic bite, and the placebo was water with added saccharine. ( 8) Both the vinegar and the placebo also had food coloring added. The intense sweetness of the test drinks in association with the bright red, blue, or green color of the drinks were intended to conceal the presence of vinegar. (We could speculate that the saccharine might have introduced a confounding variable with regard to blood glucose & insulin, but since both the vinegar group and the placebo group ingested the saccharine, we would hope that even if it did have an effect, both groups would be affected equally, essentially neutralizing any difference between the two.)
Ingesting Vinegar May Lead to Reduced Hunger
In most of the studies, postprandial blood glucose reached a lower peak and came back to baseline more quickly with vinegar ingestion than without. One of the studies’ subjects reported an increased degree and duration of satiety after the test meal with vinegar versus the one without. ( 9)
That’s fancy-speak for saying that when vinegar was included with the test meal (wheat bread providing 50 grams of available carbohydrate), the subjects felt fuller and stayed fuller for longer than when eating a meal without vinegar. I am speculating here, but perhaps the increased satiety is connected to the aforementioned better digestion: If you are digesting and absorbing more of the nutrients in your meal, it makes sense that you’d feel more satisfied and possibly have a longer sustained feeling of satiety than if some of the nutrients were being lost to suboptimal digestive function.
Vinegar Reduces Blood Glucose and Insulin
The studies that measured postprandial glucose and insulin generally showed that both of these were lower in the vinegar groups. This is important, because lower glucose at the expense of higher insulin is not necessarily a desirable thing. (10) (Even in the absence of elevated glucose, chronically high insulin appears to be a major driver of cardiometabolic disease.)
The fact that insulin was shown to be lower after meals containing vinegar suggests that the lower blood glucose is not due to increased insulin, and it may in fact be the reverse: insulin might be lower because glucose is lower. Less of a spike in glucose means less insulin is needed to clear it out of the bloodstream. So we can rule out the likelihood that vinegar lowers blood glucose by raising insulin.
How Does Vinegar Affect Glycemic Impact?
The blood glucose moderating effects of vinegar appear to depend somewhat on the food matrix in which the carbohydrate is presented. If the carbs are in liquid form and don’t even have to be broken down in order to be digested (such as in juice or sugar-sweetened beverages), then vinegar provides virtually no benefit.
A food’s glycemic index and load matter, and researchers also speculate that the amount of fiber and the ratio of amylose to amylopectin could also be a factor. ( 11)
In other words, vinegar might have more or less benefit, depending on whether the food is, for example, potatoes, bread, parsnips, beets, or beans. It might also have differing effects on the same food depending on the level of processing — such as a whole, intact baked potato versus puréed mashed potatoes that don’t even have to be chewed, or a salad of whole wheat berries as opposed to whole wheat crackers that liquefy in your mouth when you mix them with saliva for a few seconds and also don’t need to be chewed.
Taken as a whole, studies indicate that it’s not the total carb content of a meal, but rather, the degree to which the carbs need to be broken down in the digestive tract, that determines how much of an effect vinegar might have — if any.
Add vinegar to a can of soda, and good luck stopping that skyrocketing blood sugar. But dip a chunk of bread in olive oil and lots of balsamic before a pasta dinner and maybe there’s something to it. And don’t forget that adding vinegar to certain starches that have been cooked and cooled to produce resistant starch, like a potato salad or sushi rice, is another way to reduce the elevations in glucose and insulin. ( 12) If you’re following a keto or low carb diet, pasta and potatoes likely aren’t part of your life anymore, but on the rare occasion when you might choose to indulge, adding vinegar to starchier meals may help slightly attenuate the impact on blood glucose and insulin.
There’s debate among the researchers as to the actual mechanism by which vinegar results in lower glucose & insulin.
How Does Vinegar Lower Blood Glucose and Insulin?
There are two main theories:
1. Delayed Gastric Emptying
Vinegar causes food to leave the stomach more slowly, which results in a more gradual (and lower overall) rise in postprandial blood glucose. This has been demonstrated in healthy, non-diabetic subjects as well as subjects with type 1 diabetes. ( 13, ( 14)) Slower emptying of the stomach could also account for the aforementioned reported increase in satiety with vinegar ingestion.
In the arm of a study involving ingestion of a dextrose solution, vinegar had no effect on reducing PPG at any time point, which suggests that vinegar lowers glucose in part by delaying gastric emptying and/or slowing down the digestion of starch and other complex carbs, rather than that of simple sugars.
This would explain why a study evaluating the effects of vinegar in the context of an oral glucose tolerance test (OGTT) failed to show any benefits from vinegar. The study involved type 2 diabetics treated with oral glucose lowering medications who did an oral glucose tolerance test. ( 15) Average age of the subjects was 65, with an average HbA1c of 6.6, and average BMI 29.7. So this was a relatively small study group of middle-aged, overweight, not-too-poorly managed type-2 diabetics. (HbA1c of 6.6 isn’t stellar, but many diabetics have levels much higher.) The protocol had subjects drink a beverage containing 75 grams of glucose, once by itself, and then again on a separate test day taken along with 25 grams of white vinegar (4% acidity). There was basically no difference in the glucose and insulin levels with or without the vinegar. This should come as no surprise, though: they gave diabetics 75 grams of pure glucose in liquid form and 25 grams of vinegar made no difference in their glucose spike? This should shock exactly no one.
2. Inhibition of Intestinal Disaccharidases
If vinegar reduces activity of enzymes in the small intestine that digest carbohydrates, then fewer simple sugars will be absorbed, resulting in a smaller rise in PPG.
Studies on human cell lines in vitro have shown that vinegar decreases the activity of multiple disaccharidases (sucrase, maltase, lactase, and trehalase), which could certainly affect PPG. ( 16) Vinegar seems to be effective only in the presence of complex carbs, which require more digestion than simple sugars (monosaccharides). This further explains the lack of effect of vinegar when pure liquid glucose is consumed. Researchers noted, “Vinegar did not alter PPG when ingested with monosaccharides, suggesting that the antiglycemic action of vinegar is related to the digestion of carbohydrates.” ( 17)
However, even in a meal that did contain liquid sugar (in the form of orange juice), when the meal wasn’t just sugar, ingestion of vinegar was shown to help reduce postprandial glucose and insulin in healthy subjects, in type 2 diabetics, and in non-diabetic subjects with insulin resistance. When subjects consumed a test meal consisting of a white bagel, butter, and the juice (87 g total carbs), along with placebo or 20 g apple cider vinegar (in 40 g water with 1 tsp saccharine), compared to placebo, vinegar reduced the postprandial glucose and insulin in all groups. Nevertheless, vinegar or no vinegar, we have plenty of reasons not to consume liquid sugars.
Another factor with using vinegar as a blood glucose regulating adjunct is timing. According to one study, 2 teaspoons (10 g) of vinegar ingested five hours prior to a carbohydrate containing meal had no notable effect on postprandial glucose compared to placebo, while the same amount of vinegar consumed along with the test meal resulted in a 19% lowering of PPG. ( 18) Here we have modern scientific evidence supporting the wisdom of traditional cuisines that employ acidic or vinegar-based condiments, especially along with starchier meals, such as pickled ginger or kimchi served with rice, dipping bread in oil and vinegar, or a German potato salad with vinegary mustard. (See here for tasty low-carb potato salad substitutes.)
Reducing the rise in blood glucose and insulin after meals is a good reason to include vinegar in your diet. Beyond that, though, perhaps the best reason is much simpler: it’s delicious!
Carb Content of Vinegar
Most vinegars are very low in carbohydrates. After all, vinegar is acidic, not sweet. Most vinegars, such as plain white distilled, apple cider, red wine, and white wine vinegars, have 0-1 gram of carbohydrate per tablespoon.
The exception is balsamic vinegar, which is significantly sweeter tasting than other vinegars. Regular balsamic vinegar has between 4-6 grams of carbs per tablespoon. However, some of the more highly concentrated high-end balsamics, such as those available in gourmet stores and the olive oil and vinegar boutiques that are popping up everywhere, will have substantially more, especially if they’re thick and syrupy. These vinegars, which are more like glazes, could pack a carb punch as high as 8-11 grams per Tbsp.
Fortunately, with balsamic vinegar, a little goes a long way so you shouldn’t need very much to achieve the desired flavor. If a recipe calls for a tablespoon or two of balsamic vinegar, even the thicker variety, the carb count per serving will still be relatively low.
Can Vinegar Help People on a Keto Diet?
The studies evaluating the effects of vinegar on postprandial blood sugar and insulin typically employ high carbohydrate meals. Since the effects appear to be dependent on reducing the digestion of complex carbs, people on ketogenic diets might not experience results as pronounced as those of people eating higher carb diets.
However, for people who have trouble sticking to keto (not everyone’s perfect!), it’s not a bad idea to incorporate some vinegar into meals that are a bit higher in starch. And for some people, blood glucose can remain stubbornly high even when following a strict keto diet. This would be another situation where vinegar would be worth trying. Testing blood sugar at intervals after meals containing vinegar would let someone know whether the vinegar is helping.
For people who experience the dawn phenomenon (elevated fasting blood glucose first thing in the morning), taking a bit of vinegar at bedtime may help bring the morning fasting glucose down a little.
It was shown that type 2 diabetics who consumed 2 Tbsp apple cider vinegar along with 1 oz of cheese at bedtime had greater reductions in fasting glucose than subjects who consumed the cheese with water. (19) The reduction wasn’t very large (only about 4-6%), but when we’re talking about a condition that can be difficult to control even with a low carb diet, every little bit helps. This study hints at mechanisms for vinegar other than slowing gastric emptying and inhibiting carbohydrate-digesting enzymes, since subjects consumed only 1 ounce of a very low carbohydrate food. It looks like there’s room for more research to be done to uncover these other possibilities, which researchers speculate may be related to vinegar affecting skeletal muscle glucose uptake, glycogen synthesis, and gluconeogenesis in the liver.
Diabetics Beware: A Word of Caution
Vinegar can be a useful addition to a diet focused on blood glucose management. However, people with type 1 diabetes and those with type 2 diabetes who use injectable insulin must be cautious when adding vinegar to their meals: for type 1 diabetics and patients with gastroparesis (common in both type 1 and type 2 diabetes), the effects of vinegar on reducing the rate of gastric emptying may result in lower than normal post-meal blood sugar, potentially leading to hypoglycemic episodes. ( 20) According to researchers, “vinegar affects insulin-dependent diabetes mellitus patients with diabetic gastroparesis by reducing the gastric emptying rate even further, and this might be a disadvantage regarding to their glycaemic control.”
Vinegar is effective for reducing post-meal sugars in type-1 diabetics, but it may be so effective that monitoring of blood glucose should be even more diligent than usual and pre-meal insulin dosing may need to be adjusted. ( 21)
Overall, vinegar appears to be a powerful addition to the diet of anyone struggling to improve their blood sugar levels, especially after meals. In fact, researchers have noted that “vinegar may possess physiological effects similar to acarbose or metformin.” (22) Metformin works through multiple mechanisms; acarbose is a compound that inhibits at least two enzymes that break down carbohydrates in the small intestine. To learn more about the intriguing properties of vinegar with regard to blood sugar and insulin, I recommend an educational blog post written by Dr. Jason Fung: The Benefits of Vinegar – Hormonal Obesity XXVIII.
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