Fitness is on what you might call a bulking phase. As of May 2017, there were almost 10m Brits sweating away at the gym every month, according to market aggregator Leisure DB, an increase of 5.1 per cent on the previous year. The same report also values the UK gym industry at a staggering £4.7 billion. In the US, over 55 million people had a gym membership in 2015, with figures no doubt continuing to climb in the years since the data was collected.

Whichever way you look at it, fitness is big business. Bolstered by the trend for wellness, calisthenics, yoga, CrossFit, and a generally more holistic outlook, more and more men are joining the local sweat box. But, for some – dare we say, the majority – deep down, a single desire remains: the desire to bulk up, gain weight, build muscle, and fill out those T-shirts for a summer body.

Of course, for some, how to gain weight is simple: you eat a lot and lift heavy weights. For others, it can be more difficult. Hitting the gym five days a week and seeing no gains? Knocking back 4,000 calories a day, to no avail? Tried every protein powder on the shelf but nothing’s working? A number of factors could be at play (try cutting out the cardio, for example – you don’t want to burn off muscle mass if you’re trying to grow). However, Luke Grahame, muscle-bound trainer at London’s high-end private gym Roar Fitness, has one particular bugbear:

“Show me a skinny guy who can’t put on weight and I’ll show you a skinny guy who doesn’t eat enough,” he says. “Whilst genetics, exceptionally high metabolisms, and extreme ectomorphic (skinny) body types do exist and have a part to play, the number one reason that some people struggle to gain weight is simply that they don’t eat enough. It’s a common trait of so-called ‘hardgainers’ to grossly overestimate what they eat, and inversely underestimate how much food is required to build genuine muscle.”