The CostCarbs concept is simple: every gram of net carbohydrate you eat has an exercise cost. Pay the cost, and those carbs don't become body fat. Ignore it, and the biochemistry plays out on its own — usually in the direction of your waistline.

But what does that actually look like in practice? This is the beginner's guide.

Why net carbs, not total carbs?

Total carbohydrates include dietary fiber — but fiber is not digested and does not raise blood glucose. It passes through your digestive tract largely intact. The only carbohydrates that matter for the CostCarbs equation are net carbs: total carbohydrates minus fiber.

This is the number on the nutrition label you actually need to care about. An apple with 25g total carbs and 4.5g fiber has 20.5g net carbs — and that's the number that drives your insulin response and determines your exercise cost.

The exercise cost formula

CostCarbs uses a simple rate: a number of reps (or minutes) per gram of net carbs. The default starting point is:

These aren't arbitrary numbers. They're calibrated to the approximate energy cost of high-intensity exercise relative to glucose uptake — but they're starting points. As you use CostCarbs with a glucose monitor, you'll calibrate your personal formula based on how your blood sugar actually responds.

The formula in plain terms: Eat 30g net carbs → do 300 bodyweight reps (or 150 weighted reps), split across multiple exercises, within 30–60 minutes of eating. That's your cost. Pay it, and the glucose gets cleared into your muscles instead of stored as fat.

Real examples

Example 1
Bowl of white rice (1 cup cooked)
~45g total carbs · 0.6g fiber · 44g net carbs
440 repsBodyweight (10/g)
220 repsWeighted (5/g)
~44 minBrisk walk
Example 2
2 slices of sourdough toast
~36g total carbs · 2g fiber · 34g net carbs
340 repsBodyweight (10/g)
170 repsWeighted (5/g)
~34 minBrisk walk
Example 3
Medium banana
~27g total carbs · 3.1g fiber · 24g net carbs
240 repsBodyweight (10/g)
120 repsWeighted (5/g)
~24 minBrisk walk

The timing window

When you exercise matters as much as whether you exercise. The ideal window is 15–30 minutes after finishing your meal. This catches the glucose absorption curve on the way up — before blood glucose peaks, before insulin responds at full force.

Exercise in this window activates GLUT4 transporters in your muscles independently of insulin, allowing your muscles to absorb glucose directly from the bloodstream. You're intercepting the glucose before the fat-storage pathway has a chance to activate.

If you can't exercise immediately after eating, exercising beforehand still helps — it depletes glycogen so there's capacity for the incoming glucose. But post-meal is the more powerful intervention.

Rep caps and exercise selection

CostCarbs caps each individual exercise at 50 reps (bodyweight) or 25 reps (weighted). If your carb intake requires more total reps, you add more exercises rather than doing a marathon set of squats. This keeps each set manageable and Zone 4/5 achievable.

For 44g net carbs (the rice example), you'd get something like:

  1. Bodyweight squats — 50 reps
  2. Kickboxing combinations — 50 reps
  3. Jump lunges — 50 reps
  4. Burpees — 50 reps
  5. Mountain climbers — 50 reps
  6. High knees — 50 reps
  7. Squat jumps — 50 reps
  8. Push-up to plank hold — 40 reps

Intense — but spread across 8 exercises, it's the kind of circuit that takes 25–35 minutes at Zone 4/5.

Calibrating your personal formula

The 10 reps/g default is a starting point. Your actual glucose response depends on your current insulin sensitivity, muscle mass, fitness level, and the specific foods you're eating. CostCarbs lets you log your glucose before and after exercise sessions to calculate your personal clearance rate.

Someone who is highly insulin sensitive might find 7 reps/g is sufficient. Someone with higher insulin resistance might need 12–15 reps/g. The glucose monitor tells you the truth — and over time, as your fitness improves, you'll likely find your rate decreasing (meaning each rep clears more glucose).

The long game: As you build more muscle and improve insulin sensitivity, the exercise cost per gram of carbs decreases. You can eat the same amount and do less work to clear it — or eat more and still stay in balance. The goal is a body that handles carbohydrates efficiently, not permanent restriction.

Start simple

You don't need to get everything perfect on day one. Here's the simplest version of the method:

  1. After your next meal, estimate the net carbs (use the CostCarbs tracker or a nutrition app)
  2. Multiply by 10 to get your rep target
  3. Do bodyweight squats or lunges for 20–30 minutes, starting within 30 minutes of eating
  4. Notice how you feel — lighter, clearer, less of the post-meal energy crash

That's it. The rest — the calibration, the exercise variety, the glucose monitoring — layers on top once the habit is established. The core insight is just this: carbs have a cost, and movement pays it.