Buttermilk is not keto friendly in standard serving sizes. One cup of cultured buttermilk contains about 13 grams of carbohydrates, almost all from sugars. On a strict keto diet that caps daily net carbs at 20 to 50 grams, a single glass could eat up a quarter to half of your entire day’s allowance.
Carbs in Buttermilk
A one-cup serving of reduced-fat cultured buttermilk, the kind sold in most grocery stores, has roughly 13 grams of carbohydrates, 10 grams of protein, and about 5 grams of fat. Those carbs come entirely from sugars, primarily lactose (milk sugar). There’s no fiber to subtract, so the net carb count stays at the full 13 grams.
Switching between low-fat and full-fat versions doesn’t help much. The carb count stays in the 11 to 13 gram range regardless of fat content. You get slightly more fat with the full-fat version, but the lactose load barely changes.
How Buttermilk Compares to Other Dairy
Buttermilk’s carb count is similar to regular milk, which puts it in the same “not great for keto” category. The fermentation process that gives buttermilk its tangy flavor does break down some lactose, but not enough to make a meaningful difference for carb counting.
Heavy whipping cream is the go-to keto dairy for a reason. A half cup of heavy cream contains only about 3 grams of carbs, and most keto recipes call for far less than that. Sour cream, another fermented dairy product, runs about 5 grams per half cup. Both are dramatically lower in carbs than buttermilk while delivering the fat content that fits a ketogenic eating pattern.
Small Amounts in Cooking and Baking
Where buttermilk does have a place on keto is in recipes that use very small quantities. A quarter cup of buttermilk divided across a batch of 12 biscuits, for example, adds only about 0.25 grams of carbs per biscuit. That’s negligible. The tangy flavor and the way buttermilk reacts with baking soda to create lift in baked goods is hard to replicate exactly, so some keto bakers keep a carton around for this purpose.
The key distinction is between drinking buttermilk and cooking with it. A splash in a recipe spread across multiple servings is a completely different carb situation than pouring yourself a glass.
Keto-Friendly Buttermilk Substitutes
If a recipe calls for buttermilk and you want to keep carbs low, you have a few options that mimic the acidity and tanginess without the sugar load.
- Heavy cream plus acid: Mix heavy cream with a tablespoon of lemon juice or white vinegar per cup. Let it sit for 5 to 10 minutes until it thickens slightly. This gives you the tang and the chemical reaction needed for baking, with a fraction of the carbs.
- Unsweetened almond milk plus acid: The same lemon juice or vinegar trick works with unsweetened almond milk, which has about 1 gram of carbs per cup. The result is thinner than real buttermilk but works in most recipes.
- Sour cream thinned with water: Sour cream already has a similar flavor profile. Thinning it to a pourable consistency gives you a reasonable stand-in for buttermilk in dressings, marinades, and batters.
Traditional vs. Store-Bought Buttermilk
What’s sold as buttermilk in stores today is not the same product your great-grandparents would have recognized. Traditional buttermilk was the thin, watery liquid left over after churning butter. It was low in fat (since the fat went into the butter) and only mildly tangy. Modern cultured buttermilk is made by adding bacterial cultures to low-fat or whole milk, producing a thicker, more yogurt-like drink. Both versions carry a similar carb load because the base is still milk, and fermentation only converts a small portion of the lactose.
If you happen to make your own butter at home, the leftover liquid (true traditional buttermilk) won’t save you carbs. It’s thinner and less flavorful, but the lactose content remains comparable to regular milk.
The Bottom Line on Portions
Buttermilk isn’t something you need to eliminate entirely from a keto lifestyle, but it’s not a food you can consume freely. Drinking it by the glass will almost certainly push you over your carb limit for the day, especially on a strict 20-gram protocol. Using a few tablespoons in a recipe that yields multiple servings is a different story entirely, keeping the per-serving carb contribution well under a gram. If you’re tracking macros carefully, measure what you use and account for it, but don’t stress over a tablespoon in a batch of baked goods.