Fluid retention: what to eat and how to ease swelling

What is fluid retention and why does it happen?

Water is the main component of the body. Some is inside cells, while some is outside them, in the blood and in the fluid surrounding tissues. A balance of pressure in blood vessels and hormonal signals keeps the amount in each place stable.

When more fluid than usual leaves the blood vessels and stays in the tissues, oedema (fluid retention) occurs. In everyday life, it is often related to posture. After many hours standing or sitting still, the veins in your legs have a harder time returning blood to your heart, and fluid builds up in your feet and ankles. If you press the area with a finger and an indentation remains for a few seconds, this is known medically as pitting oedema.

Oedema can also be a sign of a heart, kidney or liver problem, or a side effect of some medicines, such as certain blood pressure medicines, anti-inflammatory drugs or corticosteroids. If the swelling does not go away, seek medical advice.

Which foods can help reduce fluid retention?

The key mineral is potassium. In the kidneys, it counterbalances sodium and helps the body excrete salt, and with it water, in the urine.

Adults need at least 3,510 mg of potassium a day, according to the World Health Organization [2]. Reaching this amount also helps control blood pressure. You can get it from everyday vegetables, fruit, pulses, potatoes and sweet potatoes; supplements are not needed.

There is one exception. If you have chronic kidney disease or take medicines that retain potassium, do not increase your intake on your own. This applies to some diuretics, certain blood pressure medicines and spironolactone. In these situations, blood potassium may need to be monitored [3], and your doctor or kidney specialist will adjust your intake.

How much salt and sodium can you have each day?

Adults should have less than 5 g of salt a day, or less than 2,000 mg of sodium, according to the World Health Organization [1]. That is a little less than a teaspoon. Sodium is the nutrient that most strongly promotes water retention outside cells. If you take in more than your kidneys can comfortably remove, your body holds on to fluid to keep the salt concentration in your blood stable. Some of that fluid ends up in the tissues.

European hypertension guidelines also set the limit at around 2 g of sodium a day [3]. And, except in moderate or advanced kidney disease, they recommend more potassium from fruit and vegetables to lower blood pressure [3]. If you have high blood pressure, see our practical guide to high blood pressure.

Why should you drink water if you are retaining fluid?

This is one of the questions we hear most often in consultations: if you feel swollen, should you drink less? No. Drinking less does not reduce fluid retention.

Limiting fluids only makes sense if your doctor has advised you to do so, for example because of advanced heart or kidney failure. When you drink too little, the brain releases antidiuretic hormone (vasopressin), and the adrenal glands release aldosterone. Both tell the kidneys to conserve water and salt and concentrate the urine. When you are well hydrated, the kidneys can remove what is in excess as usual.

The European Food Safety Authority sets a reference intake of 2 litres of total water a day for women and 2.5 litres for men [4]. This includes water from food, estimated at around 20% [4]. Needs may differ for older adults, during pregnancy or breastfeeding, in hot weather or when exercising. Water is the drink of choice, and homemade unsalted vegetable broths also count.

What mistakes do we see in consultations?

These three mistakes come up almost every week in consultations, and all three can prolong swelling.

• Put away the salt shaker and assume the problem is solved. Most of the sodium we eat is already in foods. If you still eat commercial bread, processed meats and ready meals, your daily sodium intake will barely fall.
• Avoid fruit because it “contains water”. Fruit provides potassium, which helps the kidneys remove excess salt.
• Celebrate losing a kilo after a “draining” tea. It is water, and it returns as soon as you eat and drink normally. The cause of the swelling is still there.

Are herbal teas or diuretic plants recommended?

Unsweetened herbal tea contributes to your daily fluid intake like any other drink. We do not recommend herbs or herbal products that promise to “drain” or “eliminate fluid”, and we do not prescribe any by name. There are three reasons not to take them on your own.

1. Mineral imbalance. Forcing increased urination without supervision can cause you to lose too much potassium or sodium, leading to low blood pressure and cramps.
2. The toxin myth. The idea that herbs “cleanse the body” has no scientific basis. The liver and kidneys already remove waste; eating well, drinking enough and resting support them.
3. Delayed diagnosis. A diuretic can mask symptoms of heart or kidney disease and delay medical care.

When swelling gets worse in hot weather, around your period or during pregnancy

Fluid retention can vary considerably with temperature and hormones. In summer, blood vessels widen to release heat and, with gravity, more fluid collects in the feet and ankles.

During the second half of the menstrual cycle, the luteal phase, changes in oestrogen and progesterone can lead to temporary fluid retention. It usually resolves on its own when your period starts.

During pregnancy, increased blood volume and pressure from the uterus on the veins in the legs make swelling of the feet and ankles very common. Our healthy eating during pregnancy guide explains how to manage it safely.

Excess weight and a sedentary lifestyle can also make it harder for blood to return from the legs. Gradual fat loss with a well-planned weight-loss plan, along with more movement, may ease the heavy feeling.