Teenagers embrace 'cut and bulk' fitness trend as experts warn of health risks

A growing number of teenagers are adopting the bodybuilding practice known as "cut and bulk" — cycling between high-calorie phases to build muscle and low-calorie phases to reduce fat — driven in large part by social media content that prizes defined musculature. While some young people say the regimes improve confidence and discipline, medical and sports professionals warn the routines can pose risks to growth, hormonal health and eating behaviour.

Hashtags such as #shreddedphysique have been viewed billions of times, and TikTok videos show boys as young as 13 and 14 flexing in school corridors. For many, the pattern begins with increased training and higher food intake to gain size, followed by weeks of calorie restriction intended to reveal a leaner, more defined appearance. The process often involves detailed calorie counting, frequent gym sessions and adherence to online plans.

Fourteen-year-old George Holland, who started weight training at 11 after watching bodybuilding online, is among those practising the cycle. Holland trains with a former Mr Universe and has competed in the National Amateur Body-Builders' Association finals, winning a bronze in the under-19s category. He described an early phase of light weights at a local leisure centre, and later increasing loads after moving to a gym he described as having a "proper gym vibe."

Holland says he eats six meals a day and balances school with a training schedule he described as "four days on, one day off, four days on." He said his current "bulking" intake is about 4,100 calories a day and that after roughly 16 weeks he will reduce calories to about 2,200 a day to begin a cutting phase. "I completely disagree with that, going to the gym when you are young is dead good for you," he told the BBC, citing mental-health and discipline benefits.

Other teenagers describe different entry points to the trend. George Hazard, now 17, began training at 12 during lockdown with a simple home setup and said gym sessions later helped his recovery after a leg-lengthening operation. He trains most nights and uses social platforms to learn techniques and nutrition tips, saying that credible creators often post links to research. "You get a feeling for what is a load of rubbish and what is good stuff," he said, while acknowledging parental and practical limits on strict diets.

Eighteen-year-old Nat Walney described an evolution from "dirty bulking" — consuming large amounts of high-calorie, low-nutrient foods — to following a more restrictive regimen that includes elements of the carnivore diet and prolonged daily fasting. Walney said he fasts for 20 hours a day and eats mainly raw meat, eggs and raw milk, describing it as an "ancestral" approach. He acknowledged that some recent guidance has cautioned against fasting, and said he would alter his diet if he began to feel unwell.

Health professionals emphasised distinctions between sensible fitness and potentially harmful extremes for adolescents. Children's dietician Lucy Upton said there is nothing inherently wrong with young people wanting to be fit, but warned the cultural focus often skews toward appearance rather than health. She said online content can conflate or misapply scientific findings, and urged viewers to scrutinise the credentials behind posts and to be wary when content promotes products or paid endorsements.

Sam Grady-Graham, a coach with GB Boxing, cautioned against restrictive eating in adolescence, noting that the growth spurt between about 12 and 18 requires a full and varied diet. "The rate of growth is exponential," he said, adding that a balanced approach to food from all main groups supports development. On training intensity, he advised prioritising technique and movement over rapid increases in load, arguing that proper movement patterns lay the foundation for long-term progress and reduce injury risk.

Sports nutritionists and clinicians also highlight the risk of muscle dysmorphia, an eating-disorder–related condition in which individuals perceive themselves as too small or insufficiently muscular despite appearance. Experts say the combination of idealised images on social platforms, quantified metrics such as body-fat percentages and calorie targets, and young people's developing relationships with food can create fertile ground for disordered behaviour.

Use of artificial intelligence tools and online forums to create personalised plans further complicates the picture. Teenagers in interviews acknowledged consulting AI chatbots for guidance; clinicians warn that such tools can produce information of variable accuracy and should not replace qualified medical or nutritional advice. Extended fasting and extreme unbalanced diets can affect organ function and hormonal maturation; prolonged fasts beyond a few days carry particular risks and should be supervised by medical professionals when considered at all.

Parents, teachers and coaches were urged to look for warning signs such as abrupt changes in eating patterns, excessive preoccupation with body image, and training that interferes with sleep, school or social life. Upton recommended assessing whether the source of nutrition or training advice is experiential or clinical, and treating commercial endorsements as a red flag.

The current trend illustrates how social media, peer groups and competitive outlets can reshape adolescent ideas about fitness. While many teenagers report benefits including improved strength and self-discipline, experts say that supporting balanced nutrition, proper training technique and open conversations about body image is essential to prevent harm as young people experiment with extreme diets and regimented training cycles.