Net carbs are total carbs minus fiber and certain sugar alcohols. Total carbs include everything. Which number you should count depends on your goal: net carbs for ketogenic diets and weight loss, total carbs for insulin dosing with diabetes. The FDA does not define or regulate “net carbs” on nutrition labels – you calculate it yourself.
The Definitions
Total carbohydrates is the line on a U.S. nutrition facts label that shows every gram of carbohydrate in a serving, including fiber, sugars, starch, and sugar alcohols.
Net carbs (also called “impact carbs” or “digestible carbs”) attempts to count only the carbs that actually raise blood glucose. The formula subtracts fiber (which passes through undigested) and a portion of sugar alcohols.
For more detail, see our what are net carbs primer and the how to calculate net carbs walkthrough.
The Net Carb Formula
Net carbs = Total carbs – Dietary fiber – (Sugar alcohols x subtraction factor)
Example: A protein bar lists 25g total carbs, 10g fiber, 5g erythritol.
Net carbs = 25 – 10 – 5 = 10 grams.
Why Fiber Is Subtracted
Fiber is a carbohydrate your small intestine cannot digest. It reaches the colon largely intact, where bacteria ferment part of it into short-chain fatty acids. Fiber:
- Does not raise blood sugar meaningfully
- Slows the absorption of other carbs when eaten together
- Provides around 2 calories per gram (vs 4 for digestible carbs)
Subtracting all 100 percent of dietary fiber is standard practice in U.S. net-carb calculations. In Canada, Europe, and Australia, labels already list “carbohydrates” as net of fiber, so no subtraction is needed there.
Sugar Alcohol Rules
Sugar alcohols (polyols) are partially absorbed and partially excreted, so their blood-sugar impact varies.
| Sugar Alcohol | Glycemic Index | Subtract for Net Carbs? |
|---|---|---|
| Erythritol | 0 | 100% – subtract all |
| Allulose | 0 | 100% – subtract all (FDA exempt from total sugars) |
| Xylitol | 13 | 50% |
| Sorbitol | 9 | 50% |
| Isomalt | 9 | 50% |
| Lactitol | 5 | 50% |
| Maltitol | 35 – 52 | 0% – do not subtract |
Maltitol is the trap. It is cheap, sweet, and used in many “low-carb” candies, but it raises blood sugar similarly to regular sugar. Treat it like table sugar.
Net Carbs vs Total Carbs: Head-to-Head
| Factor | Total Carbs | Net Carbs |
|---|---|---|
| Definition | All carbohydrates | Digestible carbs only |
| On U.S. nutrition label? | Yes (required) | No (calculation) |
| Best for keto / low-carb | Less useful – overcounts fiber | Yes – standard |
| Best for insulin dosing | Yes – safer, ADA-preferred | Acceptable if high-fiber meals |
| Best for weight loss | Works | Usually preferred |
| Best for a general healthy diet | Works | Works |
| Regulated by FDA? | Yes | No |
Which to Count for Each Goal
Diabetes (Type 1 or Type 2 on Insulin)
The ADA teaches insulin-dosing carb counting based on total carbohydrates. Fiber’s effect on blood sugar varies; counting total carbs builds in a safety margin. Advanced users may count net carbs if their insulin-to-carb ratio has been tuned for that.
Ketogenic Diet
Standard ketogenic protocols allow 20 to 50 grams of net carbs per day. Fiber is specifically allowed because it does not interfere with ketosis. Counting total carbs on keto would unnecessarily restrict leafy greens, nuts, and avocado.
Weight Loss
Either approach works. Net carbs align with most low-carb weight-loss programs (Atkins, South Beach). Total carbs is simpler for people following the prediabetes diet or a moderate-carb plan.
Type 2 Diabetes Managed Without Insulin
Net carbs are practical because fiber genuinely reduces blood sugar response. Focus on high-fiber foods to naturally lower net carbs without reducing food volume.
FDA Label Rules in the U.S.
According to the FDA, the nutrition facts label must list:
- Total carbohydrate
- Dietary fiber (subcategory of total carb)
- Total sugars
- Added sugars
Sugar alcohols are optional unless the product makes a sugar-free claim. “Net carbs” is not listed. Front-of-package claims use terms like “low carb,” “2g net carbs,” or “impact carbs” – these are marketing claims, not FDA-defined nutrients.
International Differences
In Canada, the European Union, and Australia, the “carbohydrates” line on food labels already excludes fiber. So what Americans call “net carbs” is essentially what Canadian and European labels list as “carbohydrates.” This can confuse travelers reading imported labels.
Examples: Comparing Common Foods
| Food | Total Carbs | Fiber | Sugar Alcohols | Net Carbs |
|---|---|---|---|---|
| 1 cup raspberries | 15g | 8g | 0 | 7g |
| 1 medium avocado | 17g | 13g | 0 | 4g |
| 1 slice whole-wheat bread | 17g | 2g | 0 | 15g |
| 1 Quest bar (chocolate) | 22g | 14g | 4g erythritol | 4g |
| 1 sugar-free candy (maltitol) | 10g | 0g | 8g maltitol | 10g (maltitol counts) |
| 1 cup cooked broccoli | 11g | 5g | 0 | 6g |
| 1 medium apple | 25g | 4g | 0 | 21g |
| 1 cup almonds | 31g | 17g | 0 | 14g |
Common Mistakes
- Subtracting maltitol – raises blood sugar almost as much as sugar
- Subtracting fiber when the label already deducts it (non-U.S. labels)
- Trusting front-of-package net carb claims without checking the label math
- Counting net carbs while insulin dosing without adjusting the ratio first
- Eating large volumes of sugar alcohols – can cause gastrointestinal upset regardless
The Bottom Line
Net carbs vs total carbs isn’t a winner-take-all debate. Count net carbs for ketogenic, low-carb, or general weight-loss diets. Count total carbs for safer insulin dosing, especially when starting out. Always watch out for maltitol, and remember the FDA doesn’t define “net carbs.” For more carb guidance, see our diet and nutrition hub.
