If you thought fast food was bad for the old waistline, sit-down restaurant meals in chains are no better, a new study suggests.

Comparing the calorie content of popular meals from fast food restaurants with meals from full-service restaurant chains across several countries, researchers found the calorie content of popular main meals in restaurant chains is often worse.

Only a small number of meals meet public health recommendations, the two studies in the Christmas issue of The BMJ revealed.

Dining out is becoming more common in many countries, and some studies suggest that people who eat out more frequently are at increased risk of weight gain and obesity.

To tackle the issue, Public Health England recently recommended that midday and evening meals should contain no more than 600 calories (kcal) each. But if you eat out at restaurants often, that might be easier said than done.

Researchers at the University of Liverpool analysed the calories in 13,500 main meals from 27 large UK restaurant chains – 21 of which were full-service, and six which were fast food.

They found an average of 751 kcal in main meal dishes served by fast food chains, and a whopping 1,033 kcal in dishes served by full-service restaurant chains.

[Read more: What a 400 calorie breakfast and 600 calorie lunch look like]

Only a small minority of meals met the 600 kcal public health recommendations, with 89 per cent of full-service dishes and 83 per cent of fast food dishes over this limit.

The second study unearthed similar results. A team led by researchers at Tufts University in Boston measured calories in the most frequently ordered meals in 116 full service and fast food restaurants across five countries: Brazil, China, Finland, Ghana and India, and compared them with calories in US restaurant meals.

They found an average of 809 kcal in main meal dishes served by fast food chains, and 1,317 kcal in dishes served by full service restaurant chains. Only restaurants in China served meals containing significantly fewer calories than US restaurants.

Again, only a small minority of meals met public health recommendations, with 94 per cent of full service dishes and 72 per cent of fast food dishes over the limit.

Researchers said the findings probably underestimate the number of calories consumed in restaurants because they didn’t include drinks, starters, desserts or side orders in their analyses.