What Are the Best Electrolytes to Take When You're Eating Much Less?

Reviewed and updated: 28 August 2026

The best electrolytes when you're eating much less, in one short answer

If you are looking for the best electrolytes when you're eating much less, the honest answer is that magnesium, potassium, sodium and calcium are the four that matter most, and for most people in the UK the one that slips quietly and is hardest to top up from a small plate is magnesium. Magnesium contributes to electrolyte balance and to normal muscle function, which is exactly why it comes up so often when portions shrink. The rest of the picture is mostly food and fluid, not a sachet.

I get asked about this a lot, usually by people whose appetite has dropped sharply for one reason or another and who have noticed they feel a bit off, a bit wobbly, a bit more tired than the calorie maths would suggest. What follows is the whole picture in one place: what each electrolyte does, why intake falls when you eat less, what the UK reference intakes actually are, where to get each one from food, and how to choose a supplement form that your stomach will tolerate.

The quick version

• What they are: minerals that carry an electrical charge in your body fluids. Sodium, potassium, magnesium, calcium and chloride are the main ones.
• Why they matter when you eat less: minerals travel with food. Halve the food and you tend to halve the minerals, and you often drink less too because a lot of daily fluid arrives inside meals.
• The one most worth checking: magnesium. UK reference intakes are 300mg a day for men and 270mg for women, and it is one of the first nutrients to drop in studies of energy-restricted diets.
• Food first: potassium, calcium and sodium are usually easier to keep up through what you eat and drink than through a capsule.
• One honest caution: if you feel faint, unusually weak, confused, or your heart is racing, that is a conversation for your GP or pharmacist and not something to sort out on your own with a mineral supplement.

What electrolytes actually are

The word sounds sportier than it is. An electrolyte is simply a mineral that dissolves in water and carries an electrical charge. Your body runs on those charges. Nerve signals, muscle contractions and the movement of water in and out of your cells all depend on minerals sitting at the right concentration on the right side of a cell membrane. When people talk about "electrolytes", they nearly always mean these five.

Sodium

Sodium is the main mineral in the fluid outside your cells, and it is the one that largely determines how much water your body holds on to. It is also the one nearly everyone in the UK gets plenty of, because it arrives with salt in bread, cheese, sauces and anything processed. UK guidance for adults is a maximum of 6g of salt a day, which is about 2.4g of sodium. The interesting shift when you eat much less is that sodium intake can fall genuinely quickly, because most of it was coming from the exact foods you have cut.

Potassium

Potassium is sodium's partner and sits mostly inside your cells. Potassium contributes to normal muscle function and to the normal functioning of the nervous system. The UK reference nutrient intake for adults is 3,500mg a day, and national diet surveys consistently show plenty of us falling short of that even without eating less. It comes almost entirely from plants and dairy: potatoes, beans, bananas, leafy greens, tomatoes, milk and yoghurt.

Magnesium

Magnesium is involved in hundreds of enzyme reactions, which is a dry way of saying it sits behind an enormous amount of ordinary function. Magnesium contributes to electrolyte balance, to normal muscle function, to the normal functioning of the nervous system, to normal energy-yielding metabolism and to the reduction of tiredness and fatigue. UK reference nutrient intakes are 300mg a day for men and 270mg a day for women, and the Nutrient Reference Value used on UK labels is 375mg.

Calcium

Most people think of calcium as a bone mineral, and it is, but a small and tightly controlled fraction circulates and does electrolyte work. Calcium contributes to normal muscle function and to normal neurotransmission. The UK reference nutrient intake is 700mg a day for adults. Dairy is the obvious route, but fortified plant drinks, tinned sardines with the bones in, and calcium-set tofu all count.

Chloride

Chloride rarely gets its own paragraph, because it arrives alongside sodium in salt and almost nobody needs to think about it separately. The UK reference intake is 2,500mg a day. If your sodium is reasonable, your chloride almost certainly is too.

Why electrolytes slip when you eat much less

This is the part most articles skip, and it is really the whole point. Minerals are not free-floating extras. They are dissolved in your food. When your daily intake drops from a typical plate to a much smaller one, everything on that plate drops proportionally, minerals included, unless you deliberately change what the smaller plate contains.

Research on energy-restricted diets bears this out plainly. In a randomised comparison of four popular weight-loss diets, a significant proportion of participants moved into intakes associated with a risk of inadequacy for magnesium in two of the four groups within eight weeks, alongside similar shifts for thiamine, folate, iron and vitamin E, depending on the pattern followed (Gardner and colleagues, American Journal of Clinical Nutrition, 2010). A longer randomised trial comparing a high-fibre with a low-carbohydrate pattern over 52 weeks found both groups consuming less than the adequate intake for potassium, and less than the estimated average requirement for vitamins D and E, whichever pattern they were on (Malik and colleagues, Food Science and Nutrition, 2020). Dietetic modelling of energy-restricted diets reaches the same conclusion from the other direction: several nutrients simply do not reach target unless the menu is redesigned around them (Lister and colleagues, European Journal of Clinical Nutrition, 2017).

Read those honestly and you get a useful, unglamorous message. Eating less is not automatically a mineral problem, but it becomes one if the food you keep is low in minerals. A small plate of nutrient-dense food behaves very differently from a small plate of toast and biscuits.

There is a second, quieter route as well. A meaningful share of daily fluid comes in with food, from soups, fruit, vegetables, yoghurt and sauces. Eat considerably less and your fluid intake tends to fall without you consciously drinking less. That is worth knowing, because thirst is a slow and slightly unreliable signal at the best of times.

How much of each you actually need in the UK

UK figures differ from the American ones you will find on most of the internet, and it is worth having the right numbers in front of you. For adults, the reference nutrient intakes are 300mg a day of magnesium for men and 270mg for women, 3,500mg of potassium, 700mg of calcium and 2,500mg of chloride, with sodium framed as a maximum rather than a target at no more than 2.4g a day, which is 6g of salt.

Labels use a different number again. The Nutrient Reference Value, the percentage figure printed on UK supplement packs, is 375mg for magnesium, 2,000mg for potassium and 800mg for calcium. That is why a magnesium product can read as more than 100% NRV while still sitting close to the everyday reference intake. It is a labelling convention, not a claim that you need more than everyone else.

On fluid, the European reference for total water intake is about 2 litres a day for women and 2.5 litres for men, and that total includes water arriving in food. The familiar NHS advice to aim for six to eight glasses of fluid a day is the practical version of the same idea.

Where electrolytes come from in food and drink

If you only change one thing, change what goes on the smaller plate rather than adding a sachet on top of it.

• Magnesium: pumpkin seeds, almonds, cashews, spinach, black beans, wholemeal bread, brown rice, oats and dark chocolate. Nuts and seeds are unusually concentrated, which makes them useful when volume is limited.
• Potassium: potatoes with the skin on, sweet potato, bananas, avocado, beans and lentils, tomatoes and tomato juice, mushrooms, spinach, milk and plain yoghurt.
• Calcium: milk, cheese, yoghurt, fortified plant drinks, tinned sardines and pilchards with the bones, calcium-set tofu, kale and pak choi.
• Sodium and chloride: ordinary table salt used in cooking, bread, cheese, olives, stock and miso. Most people need less rather than more, but if you have cut out most processed food at speed, salting your food normally is sensible rather than virtuous.
• Fluid: water, milk, sugar-free squash, tea and coffee all count towards the total. So does soup, which is a genuinely efficient way to get fluid and minerals into a small appetite.

A practical trick when appetite is low: make the fluid carry something. A glass of milk brings calcium, potassium and protein. A mug of soup brings sodium, potassium and water together. Plain water is fine, but it is nutritionally empty, and when total intake is small, every mouthful is worth using.

Signs your fluid and mineral balance is off

These are general signals rather than proof that anything is wrong, and there is a lot of overlap between them and simply eating too little in general.

• Dark yellow urine, or noticeably less of it than usual.
• Headache that lifts after a decent drink.
• Feeling light-headed when you stand up quickly.
• Muscle twitching or night-time cramping.
• Flat, heavy tiredness that does not match how much you have done.
• A dry mouth and dry lips through the day.

None of these on their own means a mineral is low. Poor sleep, too little food overall and simply not drinking enough will produce most of them. What I would say is that if a symptom is persistent, or if it is severe, you want a person rather than an article. Confusion, fainting, a racing or irregular heartbeat, repeated vomiting or being unable to keep fluids down are all reasons to contact your GP, NHS 111 or a pharmacist promptly, not reasons to try a stronger supplement.

Which magnesium form to choose, and why it matters more than the milligrams

This is where a lot of money gets wasted. Magnesium supplements are not one product. The mineral is always bound to something, and what it is bound to changes both how much you absorb and how your gut feels about it.

A systematic review of magnesium bioavailability studies concluded that inorganic forms appear to be less bioavailable than organic ones, and that the percentage absorbed is dose dependent, so a large single dose is absorbed proportionally less well than a smaller one (Pardo and colleagues, Nutrition, 2021). Separately, a study that put fifteen commercially available magnesium products through a simulated digestive model and then tested two of them in thirty people found a very wide spread in how much dissolved and became available, and that the products predicted to be poor in the lab were also poor in people (Blancquaert and colleagues, Nutrients, 2019). In other words, the number on the front of the pack tells you less than you would hope.

In plain terms:

• Magnesium oxide is the cheapest and the most common in budget products. It carries a lot of magnesium by weight, but it is an inorganic salt and absorbs poorly, and the portion that stays in the gut pulls water with it, which is why it has a reputation for loosening things.
• Magnesium citrate is better absorbed and works quickly, which is useful, but at higher amounts it has a similar laxative tendency for the same reason.
• Magnesium glycinate, also sold as magnesium bisglycinate, is magnesium bound to the amino acid glycine. It is well absorbed and it is the form most people find gentlest on the stomach, which is the deciding factor when your appetite is already fragile.
• Magnesium malate is bound to malic acid, a molecule that sits inside your cells' own energy cycle, and it is generally well tolerated.

My own view, and the reason our triple-form magnesium glycinate complex is built the way it is, is that combining glycinate, malate and citrate gets you good absorption without leaning the whole dose on any one pathway. It provides 384mg of elemental magnesium per two-capsule serving, which is 102% of the NRV, with no oxide and no chalk. It is made in a GMP-certified facility and tested for purity and heavy metals. If you want the longer comparison, I have written it up in more detail in our guides to magnesium glycinate versus citrate and to whether glycinate and bisglycinate are different things at all.

Shop Magnesium Glycinate 3-in-1

A simple daily routine when portions are small

Nothing here is clever. It is just the set of habits that seem to work for people eating meaningfully less than they used to.

• Drink to a schedule, not to thirst. A glass on waking, one with each meal, one mid-afternoon and one in the evening gets most people close to target without thinking about it.
• Make one drink a day nutritious. Milk, a fortified plant drink or a mug of soup will carry calcium, potassium and fluid together.
• Put minerals in the small plate. A handful of pumpkin seeds or almonds, a potato with the skin on, a tin of beans, a portion of leafy greens. Dense beats bulky when appetite is limited.
• Salt your food normally. If you have removed most processed food quickly, ordinary seasoning is not the enemy it is often made out to be.
• Take magnesium with food and in the evening if it suits you. With food improves tolerability, and many people simply find evening easier to remember.
• Give it a fair run. Mineral status changes over weeks, not over a weekend.

The wider question of which nutrients thin out first on a reduced intake, and how to cover them sensibly, is worked through in our guide to what supplements to take on a calorie deficit, and if flat tiredness is the main thing you have noticed, our guide to what vitamins help with tiredness covers the same ground from that angle.

What about sports drinks and electrolyte sachets?

They have a real use, and it is narrower than the marketing suggests. Sports drinks were designed for people losing a lot of sweat over a long period, where sodium losses are genuinely large and carbohydrate is wanted for fuel. That is a very different situation from someone eating small meals at a desk.

Two things are worth checking on the label. The first is sugar. A standard 500ml isotonic sports drink commonly carries around 15 to 30g of sugar, which is a meaningful share of a small daily intake and, for many people, an odd thing to spend it on. The second is what is actually in the sachet. Many hydration products are mostly sodium with a token amount of everything else, so a sachet advertising four electrolytes may be giving you a useful amount of one of them.

Sugar-free electrolyte tablets avoid the first problem and are perfectly reasonable if you like them, particularly in hot weather or after exercise. I would just be clear-eyed about what they are for. If your concern is a magnesium intake that has quietly halved, a sodium-led sachet is not the tool for that job.

How much is too much: the upper limits worth knowing

Minerals are not a case of more being better, and two numbers are worth carrying around.

For magnesium from supplements, the European Food Safety Authority sets a tolerable upper intake level of 250mg a day from readily dissociable salts, while the UK Expert Group on Vitamins and Minerals set a guidance level of 400mg a day for supplemental magnesium. The two bodies used different approaches and different endpoints, which is why the numbers differ. Both limits refer to supplemental magnesium only, not to magnesium from food, which is not capped in the same way because it is absorbed more slowly. The effect that sets these limits is a loosening of the bowels rather than anything dangerous, and it is dose dependent and reversible. If you are taking a higher-strength magnesium product, splitting it or taking it with food usually settles it.

Calcium has a UK guidance level of 1,500mg a day from supplements. Potassium supplements in the UK are deliberately kept low in strength, and high-dose potassium is not something to self-prescribe, particularly for anyone with kidney problems or on blood pressure medication. Sodium, as covered, is a ceiling rather than a target for most people.

A few cautions worth knowing

• Kidney problems. Your kidneys do the work of clearing excess magnesium and potassium. If your kidney function is reduced, do not take magnesium or potassium supplements without medical advice.
• Medicines. Magnesium can interfere with the absorption of some antibiotics, including tetracyclines and quinolones, and with bisphosphonates and levothyroxine. The usual approach is to separate them by a few hours, and your pharmacist can tell you the right gap for your specific medicine.
• Blood pressure and heart medication. Some medicines, including certain diuretics and ACE inhibitors, change how your body handles potassium. Do not add potassium supplements to those without your prescriber's input.
• Pregnancy and breastfeeding. Speak to your midwife, GP or pharmacist before starting a new supplement.
• Anything prescribed. If you are taking any prescribed medicine, questions about how it interacts with your diet, your fluid intake or a supplement belong with the clinician or pharmacy team who prescribed it. That is not a brush-off, it is simply the only place that advice can safely come from.

When to speak to a GP or pharmacist

Please do not use this article as a substitute for a conversation. Book one if you have persistent dizziness or fainting, a racing or irregular heartbeat, confusion, unusual weakness, ongoing vomiting or diarrhoea, or if you cannot keep fluids down. Also worth a conversation: if your appetite has dropped sharply for more than a couple of weeks and you are not sure why, or if you are losing weight quickly and feeling unwell with it. A blood test can settle in a morning what months of guessing will not.

Frequently asked questions

Do I actually need an electrolyte supplement if I am eating much less?

Most people do not need a general electrolyte sachet. Sodium, potassium and calcium are usually easier to keep up through food and drink. Magnesium is the one worth looking at, because it is concentrated in nuts, seeds, wholegrains and greens, which are often the foods that get squeezed out first when portions shrink.

Which magnesium is gentlest on the stomach?

Magnesium glycinate, also called bisglycinate, is the form most people find easiest to tolerate. Magnesium oxide is the most likely to loosen the bowels because so little of it is absorbed. Taking any magnesium with food also helps.

Can I just drink more water?

Water is the foundation, but water alone contains almost no minerals. If your food intake has fallen a long way, drinking more plain water addresses the fluid half of the picture and none of the mineral half. Pairing fluid with mineral-carrying food and drink is the more useful move.

Are sports drinks a good option?

They are designed for heavy, prolonged sweating, and most carry 15 to 30g of sugar per 500ml bottle. Sugar-free electrolyte tablets are a reasonable alternative if you like them, but check the label, because many are largely sodium with only token amounts of the other minerals.

How long before I notice anything?

Hydration changes can be noticeable within a day or two. Mineral intake works on a longer timescale, so give any change to your food or supplement routine several weeks before drawing conclusions, and keep the rest of your routine steady while you do.

What should I look for on a magnesium label?

Check the elemental magnesium figure rather than the compound weight, since 1,000mg of magnesium glycinate is not 1,000mg of magnesium. Check which forms are used and whether oxide is doing most of the work. Check the NRV percentage. And check that the manufacturer will tell you where it is made and how it is tested. Our fuller checklist is in the best magnesium supplements UK guide, and there is more on the muscle side of things in what magnesium is good for muscle function.

The bottom line

When you are eating much less, the electrolyte question is really a food question wearing a sports-science costume. Keep fluid up on a schedule, put mineral-dense food on the smaller plate, season your cooking normally, and if you want to cover one thing with a supplement, magnesium in a well-absorbed and gentle form is the sensible candidate, because magnesium contributes to electrolyte balance and to normal muscle function. Everything beyond that is a conversation with your GP or pharmacist, and I would rather you have that conversation than buy a bigger tub.

Shop Magnesium Glycinate 3-in-1

You can browse the rest of our library on the supplement guides hub, or start from the Pure Vitamins UK home page.

Dr. Miron, Founder of Pure Vitamins UK

This product is a food supplement and should not be used as a substitute for a varied, balanced diet or a healthy lifestyle. This article is for general information and is not medical advice. If you have a health concern or take prescribed medication, please speak to your GP or pharmacist.