Comparing 100 g of dry lentils with 100 g of cooked lentils can be misleading. They may look nutritionally very different, yet they are the same food before and after taking up a large amount of water. That hydration changes the weight and therefore the concentration of nutrients per 100 g.
The key point is simple: cooking does not suddenly remove most of the protein, fibre or minerals from a pulse. Some water-soluble compounds can leach out and some heat-sensitive nutrients may fall, but the largest difference on nutrition tables is usually dilution by water.
Water changes the denominator
Dry pulses contain relatively little water, so starch, protein, fibre and minerals are concentrated in a small weight. During soaking and cooking the seed absorbs water and becomes much heavier. When nutrients are then expressed per 100 g, the same nutrients are spread through a larger mass.
| Comparison | Dry pulses | Cooked pulses |
|---|---|---|
| Water | Low | Much higher |
| Calories per 100 g | More concentrated | Less concentrated |
| Protein per 100 g | More concentrated | Less concentrated |
| Fibre per 100 g | More concentrated | Less concentrated |
| Minerals per 100 g | More concentrated | Less concentrated; some can leach into water |
| Typical serving weight | Lower before cooking | Higher because of absorbed water |
This is why a dry pulse can appear to contain several times more energy per 100 g than its cooked counterpart. It does not mean cooking destroyed most of its calories; it mainly means 100 g of cooked food contains much more water.
What happens to protein during cooking?
Heat denatures proteins, changing their structure, but denaturation is not the same as disappearance. Proper cooking also lowers several protease inhibitors and other antinutritional factors and can therefore improve protein digestibility.
Protein per 100 g falls mostly because the food is heavier after hydration. Following the same batch from dry to cooked, most of the protein remains, although small amounts of soluble nitrogen compounds can move into soaking or cooking water.
What about fibre?
Fibre remains an important part of cooked pulses. Processing can alter its structure and the balance between soluble and insoluble fractions. Starch also changes with heating, and after cooling some starch can reorganise into resistant starch.
The practical point is that cooked legumes remain a high-fibre food. Their per-100-g figure is lower than in the dry state largely because water has increased the final weight.
Iron, potassium, magnesium and other minerals
Minerals are generally stable to heat; they are not destroyed in the same way as some heat-sensitive vitamins. However, minerals can leach into water. The extent depends on the pulse, soaking time, water volume and whether the cooking liquid is discarded or eaten.
A useful nutrition comparison should therefore specify whether figures refer to dry pulses, cooked-and-drained pulses, or pulses served with their cooking liquid.
Vitamins can show genuine losses
Water-soluble vitamins are more vulnerable. Some B vitamins can fall because they leach into water or are affected by prolonged heating. The exact change depends on temperature and time.
Scientific reviews describe this trade-off clearly: processing can lower certain micronutrients and phenolics while improving safety, tenderness and the reduction of antinutrients. For a wider overview, see our guide to the nutrients supplied by legumes.
How to compare dry and cooked pulses correctly
- Compare different pulses in the same state: all dry or all cooked.
- If you buy dry pulses, use dry weight when planning how much to cook.
- For canned or ready-cooked pulses, use the nutrition information for the food as sold and, where relevant, its drained weight.
- Do not interpret a lower per-100-g figure as the same percentage loss from the whole batch.
- When comparing minerals and vitamins, note whether cooking liquid was discarded.
A simple example
Imagine 100 g of a dry pulse producing roughly 240–280 g after soaking and cooking. Even if the total amount of a nutrient stayed exactly the same, its value per 100 g cooked would drop sharply because that nutrient is now distributed through well over twice the weight.
So are dry pulses more nutritious?
It is not very meaningful to call the dry food 'more nutritious' when it must normally be cooked before eating. It is simply more concentrated. Dry weight is useful for shopping and portion planning; cooked weight is more useful for describing what is actually on the plate.
Explore more practical and nutritional guides in our legumes section.
Frequently asked questions
Why do cooked pulses have fewer calories per 100 g?
Mainly because they absorb water. Their weight rises and the calories are diluted across each 100 g.
Does cooking destroy legume protein?
No. Heat changes protein structure, but most protein remains. The lower per-100-g value is largely a water effect.
Should I compare pulses dry or cooked?
Either can work as long as every food in the comparison is in the same state. Mixing dry and cooked data is misleading.
Are minerals destroyed by cooking?
Usually not by heat itself, but some minerals can leach into soaking or cooking water.
Sources and editorial approach
This guide prioritises scientific reviews on pulse processing and institutional nutrition sources. Key references include a recent review of how soaking, cooking and other processes change legumes, a review of antinutrients and traditional preparation methods, and, for iron, the NIH Office of Dietary Supplements. Exact nutrient values vary with variety, origin, storage, hydration and cooking method, so we avoid treating a single number as universal.
