The sun is shining and the mercury rising. We asked a nutritionist how we should adjust our diet during hot weather and whether you can cool off through the medium of food.
Loss of appetite, poor sleep, undulating sensations of wilting – periods of hot weather don’t always agree with us. But along with the usual precautions we should take during heatwaves – the NHS has an excellent guide to coping in hot weather – can food and drink help us out on ultra-balmy days? We spoke to nutritionist Kerry Torrens to explain how our body temperature works in relation to the weather.
How much water should we drink?
We typically lose between 2 and 2½ litres of fluid a day through sweating, breathing, urine and faeces. So on regular days we should be drinking about 6-8 glasses of water or other hydrating liquid (according to the UK Eatwell Guide). The good news is you can hit this quota through milk, sugar-free drinks, tea and coffee, as well as trusty tap water, but remember caffeinated drinks have a diuretic effect, making you lose fluids, so Kerry suggests keeping them to a minimum. Fruit juice and smoothies count too, but they should be limited to a 150ml glass daily because of the natural ‘free’ sugars they contain.
Kerry says it’s not a case of ‘one size fits all' when it comes to water intake: “Our specific needs vary depending on age, size, sex and amount of physical activity, as well as environmental factors including the temperature and humidity, both of which speed up the water lost through our skin.”
How should we adjust this in hot weather?
We should reconsider our water intake during heatwaves. Kerry says: “Higher temperatures and humidity increase the speed of evaporation from the skin which means we sweat more. Therefore we need to replenish our fluid levels more often and more frequently. How much more you need really depends on your personal circumstances as well as how active you are."
If you take regular exercise, this doesn’t have to cease during hot weather. Kerry suggests opting for sports drinks, which are formulated specifically to promote fluid uptake, so they should be more hydrating than traditional water.
Can you drink too much water?
It is possible to go the other way and drink too much, although for most people with healthy kidneys this will be managed by urinating more frequently. Kerry says: “Too much water consumed in a short space of time can lead to the kidneys being unable to maintain electrolyte balance, so the blood becomes very dilute. This has an effect on how our body functions – for example it impacts blood pressure. Hyponatraemia is a condition caused by too much water which causes sodium levels to fall dangerously low. Athletes who participate in endurance events and take on too much fluid may be at risk of this condition.
Read more about how to stay hydrated during exercise.
There may also be a medical reason why a person may retain more fluid – this might be a result of an existing kidney or heart condition. If you have any existing health conditions or you are experiencing symptoms, see your GP for advice on how much water is right for you.
What to eat
Which foods are hydrating?
Kerry says foods account for around 20-30% of our fluid intake, and there are some that contain more water than others. Certain fruit and vegetables score highly in this regard, and we should think about eating more of the following if we want to up the H2O:
Recipes with high fluid content can help towards hydration levels. Soups, stews and porridge are all good examples, and of course they can be made less wintery with the right seasonal ingredients. Our summery recipes should fit the bill nicely:
Our top summer soup recipes
Summer chicken & basil stew
Summer fish stew with rouille
Summer braised chicken with tomatoes
Porridge with blueberry compote
Cardamom & peach quinoa porridge
Green rainbow smoothie bowl
Can food and drink help us cool off?
Ice-cold lollies, slushies and ice cream might seem like natural choices when you want to cool off, but they may actually do more harm than good. “Cold food and drinks might give you an initial cooling effect but it’s short-lived,” says Kerry. “That’s because consuming food leads to an increase in temperature as the process of digestion is heat-generating. This combined with the rapid cooling initiated by cold food and drinks means your body over-compensates by increasing your core temperature. So you may actually end up feeling hotter than you did to start with!” That sorbet doesn’t sound so appetising after all…
Drinking something hot on a sunny day might feel like the least appealing thing to do, but warm drinks can actually help regulate your body temperature. Kerry says: “Hot drinks make your core temperature rise and that makes your body want to cool down so you sweat more to lose heat through your skin.” ‘Thermogenic’ foods like spices and chilli also increase body temperature as they kick-start our metabolism. This promotes sweating, which has a cooling effect.
Are there foods we should avoid?
Foods that require more effort to digest – like those high in protein, sugar and fibre - are thought to generate more body heat. One way of mitigating this is to use citrus-rich marinades on meat to break down the protein structure and soaking grains to help make the fibre more digestible.
Go with your gut
What happens to our digestive and appetite system when we’re hot?
If you don’t feel like eating as much in the summer, you’re not alone. “Seasonal changes including temperature and the number of daylight hours are thought to influence our appetite,” says Kerry. “In the summer our appetite tends to be reduced, especially when we’re feeling hot. One reason for this is that the body tries to regulate our body temperature by cutting down on heat-generating functions like the digestion of food."
While this kind of drop in appetite might be out of our control, we can help ourselves by ensuring the food we do eat is packed with the right nutrients. Our health & nutrition section has lots of advice on eating well, plus read our guide to eating for better digestion and discover the ultimate recipe for good gut health.
How can we stay cool at night?
Our guide to getting a good night’s sleep gives some general advice on dietary choices, but when the weather is hot, our thirst is more likely to keep us awake. Kerry says: “Many people stop drinking fluids in the evening because they don’t want to be disturbed by bathroom breaks during the night – but being dehydrated will also cause you to wake, so make sure you are not thirsty at night and keep a glass of water by the bed.”
A hot water bottle filled with icy water will cool bed linen and might help keep temperatures down, too.
Now we’re equipped with all the right tips, all that’s left to do is keep our fingers crossed for sunshine…
How do you handle heatwaves? We’d like to hear how it changes the way you eat...
This article was updated on 24 June 2019 by Kerry Torrens.
A qualified nutritionist (MBANT), Kerry Torrens is a contributing author to a number of nutritional and cookery publications including BBC Good Food magazine. Kerry is a member of the The Royal Society of Medicine, Complementary and Natural Healthcare Council (CNHC), British Association for Applied Nutrition and Nutritional Therapy (BANT).
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