Personal trainer Sam Hayward, who lost 17 stone, has revealed that weight gain during a heatwave is caused by water retention, not fat gain. In a TikTok video, he urged people not to panic if the scales show a higher number during the current record-breaking heatwave.
Why Weight Gain Occurs
The UK is experiencing extreme temperatures, with a rare red alert issued across parts of Wales and England. Schools have closed, and trains face cancellations. Temperatures are expected to reach 36°C on Wednesday and 39°C on Thursday, possibly climbing to 40°C. Hayward explained that when the body is dehydrated and hot, it thinks a drought is occurring and releases hormones to hold water.
“When you're dehydrated and that hot, your body thinks we're in a drought. So it ramps up a load of hormones, causing us to hold as much water as possible and to keep us cool,” Sam said.
The Role of Aldosterone
To combat dehydration from excessive sweating, the body releases aldosterone, which instructs the kidneys to retain water and sodium. This increases fluid volume, leading to a temporary rise in body weight. The effect subsides once the body acclimatises or temperatures cool.
Blood vessels near the skin dilate to disperse heat, causing excess fluid to seep into tissues, resulting in swelling in hands, ankles, and stomach. This also eases when temperatures drop.
Dietary Changes Aggravate Retention
Warmer weather often leads to increased consumption of salty snacks, sugary drinks, and alcohol, which aggravate fluid retention. “So don't be surprised if over the next couple of days, you gain a handful of pounds. It's nothing. It's just water. Once the weather resumes back to normal, you'll be fine,” Sam said.
