How many carbs are in mashed potatoes?
One cup of mashed potatoes has about 37g of carbohydrate and 34g of net carbs. Mashed potatoes have one of the highest glycemic indexes of any cooked vegetable preparation.
Carbs by portion
| Portion | Total carbs | Fiber | Net carbs |
|---|---|---|---|
| 1 cup mashed (210g) | 36.9g | 3.1g | 33.7g |
| 100 grams | 17.6g | 1.5g | 16.1g |
Net carbs
One cup of mashed potatoes has about 34g of net carbs, which is total carbs (37g) minus fiber (3g). Mashing breaks down the potato's cell structure, which makes the starch more accessible to digestive enzymes and raises the glycemic index compared to boiled or baked potatoes. See the net carbs guide.
Glycemic index of mashed potatoes
The glycemic index of mashed potatoes is about 87. Mashed potatoes have the highest glycemic index of any common potato preparation. The mechanical mashing ruptures cell walls and accelerates starch digestion. Instant mashed potato powder runs even higher, above 90.
For diabetes
One cup of mashed potatoes is about 37g of carbs with a GI of 87. This is a very fast blood sugar rise for a savory side dish. Adding butter and cream lowers the GI somewhat because fat slows gastric emptying. Incorporating pureed cauliflower (50/50 with potato) cuts carbs in half while maintaining a similar texture. If mashed potatoes are part of a larger meal with meat and non-starchy vegetables, the overall meal GI is lower than the potato alone. See the diabetes carb-counting guide.
Keto and low carb
One cup of mashed potatoes has about 34g of net carbs, well over a full strict keto day's budget. Mashed potatoes do not fit keto. Mashed cauliflower (about 3g of net carbs per cup) is the standard substitute.
Good to know
Instant mashed potatoes are made from dehydrated potato flakes and have an even higher GI than homemade because the potato cells are further disrupted during processing. Homemade mashed potatoes made with cream, butter, and skin-off Idaho potatoes are the most common American version. Leaving the skins in (rustic style) preserves about 2g of fiber per cup and slightly lowers the GI. Garlic mashed potatoes and cheese-topped mashed potatoes do not meaningfully change the carb count but add fat that moderates the spike.
Full nutrition (per 100g)
- Calories: 83.0 kcal
- Carbohydrate: 17.57g
- Fiber: 1.5g
- Sugars: 1.48g
- Protein: 1.91g
- Fat: 0.57g
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Get the appFrequently asked questions
How many carbs are in mashed potatoes?
One cup of mashed potatoes (210g) has about 37g of carbohydrate. A half-cup serving has about 18g of carbs.
What is the glycemic index of mashed potatoes?
About 87, which is very high. Mashed potatoes raise blood sugar faster than almost any other potato preparation because mashing breaks down the starch structure.
Are mashed potatoes keto?
No. One cup has about 34g of net carbs. Mashed cauliflower is the standard keto substitute with about 3g of net carbs per cup.
Do butter and cream lower the carbs in mashed potatoes?
They do not lower the carb count, but fat slows gastric emptying, which blunts the glucose rise. Heavily buttered mashed potatoes have a lower real-world GI effect than plain mashed.
Are instant mashed potatoes higher GI than homemade?
Yes. Instant mashed potato powder has a GI above 90 because the potato cells are broken down further during processing, making starch even more accessible.