Science · Education
How rehydration works: sodium cotransport
Why salt and sugar sit together in rehydration salts, what "water follows sodium" means, and where amino acids come into the science. Third-person physiology, in plain English.
In the small intestine, sodium is carried across the gut wall by transporters that move it together with a partner molecule, most famously glucose. As sodium and its partner are absorbed, water follows by osmosis. This is the principle behind oral rehydration solutions. Researchers have also studied amino acids, such as glycine and alanine, as sodium partners.
- SGLT1 is the best-known transporter: one carries sodium and glucose together.
- Oral rehydration salts are medical products for illness. Follow NHS or pharmacist advice.
- This page is general science. It makes no claim about any daily electrolyte drink, including Lula.
What "cotransport" means
Water cannot be pumped directly. The body moves it by moving dissolved particles, and water follows them by osmosis, towards where they are more concentrated.
In the gut lining, some transport proteins carry two things at once. The best-known example, SGLT1, carries sodium and glucose together into the cells lining the small intestine. From there the sodium is moved on into the body, and water follows the particles across the gut wall.
That is why textbooks describe sodium uptake as "coupled". Salt on its own is taken up less efficiently through this route than salt arriving with its partner.
History
The idea behind oral rehydration salts
Oral rehydration therapy is often described as one of the major medical advances of the twentieth century. It put sodium-glucose cotransport to practical use: a simple mix of salts and glucose in water to replace fluid lost through illness.
- Rehydration salts are a medical product, used for fluid loss from diarrhoea and vomiting.
- The NHS advises pharmacy rehydration sachets in those situations, and medical help if symptoms are severe.
- Daily electrolyte drinks for healthy, active people are a different thing, for a different use.
General education, not medical advice. If you are unwell and losing fluids, speak with a pharmacist, call NHS 111 or see your GP.
Where amino acids come in
Glucose is not the gut's only sodium partner. Separate transport systems carry sodium together with certain amino acids. Studies of the human small intestine have measured sodium and water uptake alongside glycine and alanine, and researchers have tested amino acid versions of rehydration solutions in clinical settings.
That research is part of why some electrolyte powders, including Lula, pair minerals with amino acids instead of loading sugar. It is not evidence that any particular product hydrates faster, better or differently, and we make no such claim for Lula.
What this means for sports drinks
The same principle explains why so many sports drinks combine sugar with salts. For long, hard efforts, the carbohydrate is also fuel. For an everyday glass, many people would rather leave the sugar out, which is why sugar-light electrolyte powders exist.
For the labels side by side, see electrolyte powder vs sports drinks.
Sources
- StatPearls: Electrolytes. NCBI Bookshelf NBK541123.
- Potency of oral rehydration solution in inducing fluid absorption is related to glucose concentration. Scientific Reports, 2020.
- The effect of amino acids and dipeptides on sodium and water absorption in man. Gut. PMC1412578.
- Absorption of glycine and L-alanine by the human jejunum. PMC292823.
- Clinical trials of improved oral rehydration salt formulations: a review. PMC2486731.
- NHS: Dehydration (nhs.uk/conditions/dehydration).
Good to know
Questions, answered
Why do rehydration drinks contain sugar?
In the gut, sodium is carried across the gut wall together with glucose by a transporter called SGLT1, and water follows by osmosis. Oral rehydration salts use that principle.
What does "water follows sodium" mean?
Water moves by osmosis towards where dissolved particles are more concentrated. When sodium is absorbed, water follows it across the gut wall.
Do amino acids help the gut take up sodium?
Researchers have measured sodium and water uptake alongside glycine and alanine in the human small intestine. That is general physiology. We make no claim that Lula's amino acids do anything for you.
Is Lula an oral rehydration solution?
No. Lula is a daily electrolyte food supplement for active people. It is not a treatment for dehydration or illness.
What should I drink if I am dehydrated from illness?
Follow NHS advice: pharmacy rehydration sachets are recommended for fluid loss from vomiting or diarrhoea. Get medical help if symptoms are severe.
Is this medical advice?
No. It is general education. Speak with a pharmacist or GP about illness.
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