Does almond or oat milk break a fast?

Plant milks compared

Milk, unsweetened	A splash, 30 ml	A cup, 240 ml	Protein per cup
Almond	About 6 calories	About 46 calories	1.6 g
Oat	About 14 calories	About 115 calories	1.9 g
Soy	About 11 calories	About 91 calories	8.5 g
Whole cow's milk, for comparison	About 18 calories	About 146 calories	7.6 g

Almond and oat: why they differ

Unsweetened almond milk is mostly water with a little almond: very few calories, little protein and little sugar. Oat milk is made from a grain, so it has more carbohydrate, about 5.6 g of sugars in a cup even when it's unsweetened ¹. Soy milk is lower in calories than oat but has far more protein, close to dairy, and protein raises insulin as well as sugar does ^2,3.

Splash or latte?

• A splash in black coffee or tea: a small trade-off many people accept, as with dairy milk.
• A latte, flat white or cappuccino: a cup's worth of milk, so it ends the fast. Have it in your eating window.
• Sweetened, vanilla or barista versions: these often contain added sugar or oil. Check the label, because sugar is the clearest fast breaker of all.
• Creamers: many are mostly sugar and oil. Treat them as food.

What we know, and what we don't

No study has measured whether a splash of plant milk changes a fast in a meaningful way. What's known is how its ingredients behave: sugar and protein raise insulin, and fat adds calories ². A few calories of unsweetened almond milk are unlikely to matter much. If a splash is what makes your morning coffee possible, it's a fair trade.

MYTH

Oat milk is the healthy choice, so it's fine while fasting.

FACT

Healthy and fasting-friendly aren't the same thing. Unsweetened oat milk has about two and a half times the calories of unsweetened almond milk, mostly from carbohydrate ¹. It's a fine choice in your eating window.

The cleanest coffee

For the cleanest fast, drink coffee black. Caffeine nudges fat release in the same direction as the fast ⁴, and up to about four 240 ml (8 oz) cups a day is considered safe for healthy adults ⁵. If you're used to milky coffee, try cutting the splash a little each week.

Sources

1. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central: Almond milk, unsweetened, plain, refrigerated (FDC ID 2257045); Oat milk, unsweetened, plain, refrigerated (FDC ID 2257046); Soy milk, unsweetened, plain, shelf stable (FDC ID 1999630); Milk, whole, 3.25% milkfat (FDC ID 171265). fdc.nal.usda.gov/
2. Holt SH, Miller JC, Petocz P. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. Am J Clin Nutr. 1997;66(5):1264-76. doi.org/10.1093/ajcn/66.5.1264
3. Nilsson M, Stenberg M, Frid AH, et al. Glycemia and insulinemia in healthy subjects after lactose-equivalent meals of milk and other food proteins: the role of plasma amino acids and incretins. Am J Clin Nutr. 2004;80(5):1246-53. doi.org/10.1093/ajcn/80.5.1246
4. Acheson KJ, Gremaud G, Meirim I, et al. Metabolic effects of caffeine in humans: lipid oxidation or futile cycling? Am J Clin Nutr. 2004;79(1):40-6. doi.org/10.1093/ajcn/79.1.40
5. Wikoff D, Welsh BT, Henderson R, et al. Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. Food Chem Toxicol. 2017;109(Pt 1):585-648. doi.org/10.1016/j.fct.2017.04.002