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Could your diet be causing your fluid retention?

Do your legs feel tired and heavy towards the end of the day? Do you feel like you retain fluid? You’re not alone. Every GP has lots of consultations with people who feel bloated or full of fluid.

Sometimes, fluid retention can be a sign of a serious medical condition, including heart failure or chronic kidney disease.

But more often the fluid is relatively mild – although it can still be a real cause of discomfort. Your hormones may play a part – if you’re a woman, it’s common to feel bloated coming up to your period. If you stand for long periods in hot weather in particular, fluid can leak from the blood vessels in your legs, leading to swollen ankles.

And you may be surprised to hear that fluid retention is often down to what you eat.

Salt and fluid

We all need some salt in our diet. Traditional salt is made up of about 40% sodium and 60% chloride. It’s the sodium that binds to water in your body, helping maintain the fluid balance in your cells. It also helps your muscles to contract and relax as well as playing a part in nerve impulses.

But most of us eat far more salt than we need. Adults shouldn’t have more than a teaspoon a day (about 6 grams) from all sources – that includes salt you add at the table and salt already in the food you eat. On average, however, adults in England are consuming 8.4 grams a day – that’s 40 percent higher than the national guideline.

Too much salt in your system leads your body to retain more water in your blood vessels. This in turn raised the pressure in your circulation, increasing the chance of high blood pressure. And high blood pressure is one of the major risk factors for heart attack and stroke. In fact, it’s estimated that high salt intake can increase your risk of stroke by almost a quarter (23%) and your risk of cardiovascular disease by 14% (1).

But there are also lots of scientific studies that suggest salt could also be playing a part in fluid retention and bloating.

Is salt really responsible for fluid retention?

It can be difficult to work out what’s really the cause of fluid retention. For instance, if your diet is high in salt, there’s a good chance that salt comes largely from ultra-processed foods. These foods are often also high in refined carbs and unhealthy fats, which can lead to weight gain and make you feel sluggish.

One pair or interesting studies tried to drill down to see whether salt – rather than any other ingredients in the diet – had a role to play in fluid retention (2) . They looked at two groups of patients – one of healthy volunteers, one of surgical patients. The people in the study were given just fluids, along with two levels of sodium. The lower level was similar to a healthy sodium intake: the second amount was three times higher.

In both cases, the researchers reported that the extra sodium led to ‘prolonged fluid retention’ compared to fluids which contained healthy sodium levels. This was the case even in people with normal kidney function.

Another study (3) shows that high salt consumption could be a culprit not just in fluid retention but also in how often you need to get up at night to wee. The researchers looked at men over 60 who had prostate issues (either enlarged prostate gland or possible prostate cancer). They kept a careful record of how much salt and fluid they took in. They compared this with how much urine they passed when, and how swollen their legs were.

The results showed the higher the men’s salt intake, the more swollen their legs were towards the end of the day. Higher salt intake didn’t affect the amount of urine they passed over 24 hours. But interestingly, there was a clear link between more salt and how much water they passed overnight.

Up in the air

Scientists have even gone above and beyond (4), testing the impact of salt intake in simulated space missions. Here, they were able to control their food intake very precisely, and altered just their salt intake. They found salt intake affects your release of natural body steroids, called mineralocorticoids and glucocorticoids. Surprise, surprise – more salt meant more retention of body water.

So if you want to reduce your fluid retention, it makes a lot of sense to look to your diet.

Top tips for reducing your salt intake

• Go back to scratch. Processed and pre-prepared foods are the biggest source of sodium in our diets (5). If you’re cooking from scratch, you know exactly how much you’re adding to your food.
• Spice up your life. Rather than adding salt to cooking, flavour food with spices, garlic (or garlic powder) and lemon juice.
• Don’t be preserved. Meats like bacon, ham, salamis, sausages etc are often very high in sodium.
• Can, can okay? Fresh and frozen vegetables are low in sodium but so are many canned vegetables. Check the label to see they’re in just water, rather than having salt (and sometimes sugar) added.
• Beware hidden salt. It’s not just foods that taste salty, like salted crisps and peanuts, that are packed with salt. Some cheeses, sauces (ketchup, soy sauce pickles etc), olives, packaged bread and even some breakfast cereals are surprisingly high in salt.
• Rock, sea, table? Lots of people believe that rock and sea salt is a ‘healthier’ alternative to table salt. In fact, all of them have the same ingredients and the same level of sodium – no matter what the price tag!
• Switch to reduced. If you do want the taste of salt, switch to a reduced sodium alternative such as LoSalt. LoSalt contains 66% less sodium than traditional sea, rock or table salt

1. Strazzullo P et al. Salt intake, stroke, and cardiovascular disease: meta-analysis of prospective studies. BMJ 2009;339:b4567 https://www.bmj.com/content/339/bmj.b4567
2. Van Regenmortel et al. Effect of sodium administration on fluid balance and sodium balance in health and the perioperative setting. Extended summary with additional insights from the MIHMoSA and TOPMAST studies. Crit Care 2022:67:157-165.
3. Yoshikawa M et al. Daily salt intake is associated with leg edema and nocturnal urinary volume in elderly men. Neurourol Urodyn 2020;39(5):1550-1556.
4. Rakova N et al. Increased salt consumption induces body water conservation and decreases fluid intake. J Clin Invest. 2017; 127(5): 1932–1943. https://pubmed.ncbi.nlm.nih.gov/28414302/
5. Allison A et al. Adoptable Interventions, Human Health, and Food Safety Considerations for Reducing Sodium Content of Processed Food Products. Foods 2018; 7(2): 16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5848120/