Why do some meals keep you fuller than others at the same calories?
Meet the ISE™ index — a clear, science-based tool to understand satiety, design meals, and upgrade your nutrition plans.
Why talk about “Satiety per calorie”?
We eat primarily to get energy (in kilocalories), but we stop eating mostly when the stomach is full. That’s why two 800-kcal meals can lead to very different satiety.
- 1 gram of fat provides 9 kcal without adding stomach volume,
- 1 gram of water adds zero calories but takes up space.
The more water and fibre a food contains, the more stomach space it occupies without pushing calories up.
The goal of ISE is to quantify how much a meal satiates per unit of energy.
We add the components that “fill” the stomach or trigger satiety:
- Water (mechanical filling) → weight 1
- Protein (hormonal signals) → weight 2
- Fibre (volume + slower gastric emptying) → weight 4
Then we divide by total kcal to get a yield.
Multiply by 100 so the numbers are easy to read (≈ 40–300).
Fat and sugar aren’t in the numerator because they add a lot of kcal with minimal volume; they automatically pull the ratio down.
The Hydro-Caloric Ratio (HCR)
≥ 5 g/kcal
Ultra hydrating
2 – 4.9 g/kcal
Hydrating
1 – 1.9 g/kcal
Classic
< 1 g/kcal
Dense / dry
Case study
“Watermelon 500 g” vs “Watermelon 500 g + Lamb chop 250 g”
| Watermelon 500 g | Lamb chop 250 g | MEAL TOTAL | |
|---|---|---|---|
| Water (g) | 455 | 145 | 600 |
| Protein (g) | 3.5 | 64.3 | 67.8 |
| Fibre (g) | 2.5 | 0 | 2.5 |
| kcal | 195 | 600 | 795 |
Calculations
| Index | Formula | Watermelon only | Combined meal |
|---|---|---|---|
| HCR | Water ÷ kcal | 455 / 195 = 2.33 | 600 / 795 = 0.76 |
| ISE | (Water + 2P + 4F) ÷ kcal × 100 | (455 + 7 + 10) / 195 × 100 ≈ 242 | (600 + 136 + 10) / 795 × 100 ≈ 94 |
Interpreting the results
| Watermelon only | Watermelon + Lamb chop | |
|---|---|---|
| Hydration | Hydrating (HCR 2.33) | Dense / dry (HCR 0.76) |
| Satiety | Very satiating (ISE 242) | Moderately satiating (ISE 94) |
Key takeaway: the lamb chop drives kcal way up but adds almost no water or fibre.
The “satiety per kcal” yield collapses → lower indices.
How to explain this in coaching
Picture a hot vegetable soup: light, rich in water and fibre. It takes a lot of stomach space for very few calories — like a big tank filled with air and water.
Now add a slice of full-fat cheese or buttered bread: the total volume barely changes, but energy density spikes. In other words, you just added a lot of “fuel” without increasing the “volume”.
“That’s exactly what ISE shows: when you add a highly energy-dense food to a water- and fibre-rich meal, calories jump while satiety per calorie drops mechanically.”
Think of ISE like a “price per kilo” applied to satiety: if you mix a very calorie-expensive food with a cheap-in-volume food, the average collapses. A small addition of a dense item can drag down the meal’s overall balance.
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Practical applications
Balance a “dry” plate
- Reduce the portion of the dense food
- Add vegetables, fruit, whole grains (water + fibre)
“You’re hitting your protein target but you’re short on water and fibre per 100 kcal. Let’s add 200 g steamed veg: same protein, HCR back > 1, and ISE above 130.”
Index limitations
- Doesn’t replace micronutrient density (vitamins, minerals).
- Doesn’t rate hedonic satiety (texture, flavour, chewing time).
Mini-quiz (self-check)
Key takeaways
- ISE and HCR are ratios.
When you add a dense, low-water/low-fibre food, both drop. - Protein matters (×2), but fibre (×4) and water (×1) drive most of the filling volume.
In practice: a solid meal combines ➜ water + fibre + sufficient protein with a controlled energy density.
Free training: Understand ISE™
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