Episode 2 | Ask the Expert | Guest: Jenaed Ruddock – Registered Sports Dietitian, Founder, Nutrition & Co
Most people understand that exercise requires energy. What fewer people appreciate is the full picture: how much energy the body needs simply to function, how quickly a mismatch between intake and expenditure creates problems, and how often those problems go unrecognised for months or even years.
In this episode of the London Bridge Sports Medicine podcast, Dr Ajai Seth is joined by Jenaed Ruddock, internationally recognised sports and performance dietitian and founder of Nutrition & Co, to explore energy balance in active people – what it is, what goes wrong when it’s disrupted, and what good fuelling actually looks like day to day.
What do we mean by energy?
Energy, in physiological terms, means far more than the ability to exercise. Every organ in the body requires energy to function. The brain accounts for roughly 20% of daily energy expenditure. The heart beats on energy. Digesting food requires energy. Even blinking and fidgeting are forms of energy expenditure.
Jenaed frames energy requirements across three main areas:
- Maintaining essential physiological functions – the baseline the body needs simply to stay alive
- Enabling physical activity and movement – from formal exercise to everyday movement
- Growth and repair of tissues – particularly important during injury, illness, and specific life stages
The practical implication is that energy requirements are always higher than most people estimate – and always higher when someone is training, recovering, or unwell.
Where does energy come from?
Energy comes from food – specifically from the three macronutrients: carbohydrates, protein, and fat. Each is broken down into its component form (glucose, amino acids, and fatty acids respectively) and used to fuel different processes at different intensities.
Fat provides the most energy per gram – nine calories, compared to four for both protein and carbohydrate. But fat is not the body’s preferred fuel source. That distinction belongs to carbohydrate, particularly at high exercise intensities, where glucose is the most efficient and accessible fuel available. “The theory of doing a high intensity session fasted is very much a myth and actually quite detrimental to energy levels,” says Jenaed.
Water is essential but not a source of energy. And despite what might seem an appealing idea, sunlight provides no meaningful energy for human physiology beyond supporting vitamin D synthesis.
What happens when we don’t have enough energy?
When energy going out consistently exceeds energy coming in, the body goes into a form of preservation mode. This has wide-ranging consequences – and most of them are not immediately obvious.
Jenaed outlines the key effects of energy deficiency in active people:
- Impaired growth and tissue repair – the body cannot rebuild what training breaks down
- Increased injury risk – including stress fractures, which occur when bone repair falls behind bone stress
- Hormonal disruption in females – missed or irregular menstrual cycles, as the body deprioritises reproduction in favour of survival
- Weakened immune function – insufficient nutrients to maintain immune defences
- Deteriorating bone health – inadequate calcium and vitamin D availability
- Reduced training adaptation – the session essentially becomes wasted; the body cannot generate the adaptations it is training for
This cluster of symptoms is formally recognised as Relative Energy Deficiency in Sport (RED-S) – a condition that affects both male and female athletes across all levels of sport. One of its defining characteristics is that it often goes unrecognised for a long time: symptoms accumulate gradually and many – fatigue, lower mood, performance plateaus – are easily attributed to other causes.
Who is most at risk?
Certain groups are at significantly higher risk of energy deficiency, and Jenaed is clear that this is not simply about people who are dieting. The populations she sees most frequently include:
- People with eating disorders or disordered eating – including those with orthorexia (an obsessive focus on “healthy” eating) and those who over-exercise as part of a restrictive pattern
- Adolescent female athletes – under significant social pressure around weight, training hard, and often unaware of how much they actually need to eat
- Older adults – reduced appetite, altered taste, and difficulty swallowing can all reduce intake below requirements
- People recovering from injury – one of the most common and counterintuitive risk scenarios: when injured athletes can’t train, they often cut back on food, not realising that tissue repair significantly increases their energy needs
- Pregnant and lactating women – energy requirements are meaningfully higher and not always met
Dr Seth adds the clinical observation that many patients presenting with injuries turn out to be energy deficient without any awareness of it. The connection between what they’re eating and the injury they’re dealing with is rarely something they’ve considered.
The carbohydrate question
“Everyone loves to hate the carb,” says Jenaed – and she has seen the consequences of that in clinic. Carbohydrate is the body’s preferred fuel source for exercise, particularly at higher intensities. Restricting it in the context of active training is not a neutral choice; it means either underperforming or forcing the body to use less efficient fuel sources.
The exception is weight-category sports, where some athletes may use short-term carbohydrate reduction to make weight. But Jenaed is clear: this is a highly specific, closely managed intervention, not a general lifestyle recommendation. Boxers making weight will tell you exactly how they feel during that phase. It is not a model to emulate.
Low carbohydrate eating can still provide adequate total calories, but it will not support optimal performance in high-intensity sport, and it does not need to be the default for the vast majority of active people.
Practical fuelling: what it looks like
The plate model
For moderate intensity training, Jenaed recommends building meals around the following proportions:
- One third carbohydrate – pasta, rice, quinoa, bread, legumes
- One third protein – meat, fish, eggs, dairy, pulses
- One third vegetables – plus a small amount of healthy fat (avocado, oils, nuts, seeds)
For higher training loads or twice-daily sessions, the carbohydrate proportion should increase – up to half the plate. The body’s needs change with its demands.
Fuelling around exercise
- Before training: a quick-release carbohydrate snack – fruit, fruit juice, or a simple carbohydrate – particularly for sessions lasting over 45 minutes at high intensity
- During training: for sessions over an hour, a carbohydrate solution drink with electrolytes maintains fuel availability
- After training: carbohydrate and protein together – at a ratio of approximately 3:1. Chocolate milk is a frequently recommended and well-evidenced option for post-training recovery
General habits
- Don’t skip meals – the hunger cycle runs on a two-to-four hour rhythm, and gaps larger than that work against energy regulation
- Include two snacks daily – particularly when training volume is high. Three meals a day is often not enough for active people
- Stay hydrated – but don’t confuse hydration with fuelling; water supports physiology but does not replace food energy
- Don’t fear rest days – the body recovers, repairs, and adapts on rest days. Fuelling them appropriately is as important as fuelling training days
- Recognise when restriction is a problem – and seek professional support if eating patterns feel difficult to change
The bottom line
Energy deficiency in sport is common, underdiagnosed, and frequently self-inflicted without any awareness. The consequences range from reduced training adaptation – essentially wasted sessions – through to serious health effects including stress fractures, hormonal disruption, and compromised immune function.
The solution is not complicated in principle: eat enough, eat regularly, fuel around exercise, and stop treating carbohydrate as the enemy. “Food is your toolkit,” as Jenaed puts it. The right tools make the job possible. Without them, the body does the best it can with what it has – and the gaps show up, eventually, as injury, fatigue, or stalled progress.
If you are unsure whether your nutrition is keeping pace with your training, a consultation with a registered sports dietitian is the most effective way to find out.
Most people understand that exercise requires energy. What fewer people appreciate is the full picture: how much energy the body needs simply to function, how quickly a mismatch between intake and expenditure creates problems, and how often those problems go unrecognised for months or even years.
In this episode of the London Bridge Sports Medicine podcast, Dr Ajai Seth is joined by Jenaed Ruddock, internationally recognised sports and performance dietitian and founder of Nutrition & Co, to explore energy balance in active people – what it is, what goes wrong when it’s disrupted, and what good fuelling actually looks like day to day.
What do we mean by energy?
Energy, in physiological terms, means far more than the ability to exercise. Every organ in the body requires energy to function. The brain accounts for roughly 20% of daily energy expenditure. The heart beats on energy. Digesting food requires energy. Even blinking and fidgeting are forms of energy expenditure.
Jenaed frames energy requirements across three main areas:
- Maintaining essential physiological functions – the baseline the body needs simply to stay alive
- Enabling physical activity and movement – from formal exercise to everyday movement
- Growth and repair of tissues – particularly important during injury, illness, and specific life stages
The practical implication is that energy requirements are always higher than most people estimate – and always higher when someone is training, recovering, or unwell.
Where does energy come from?
Energy comes from food – specifically from the three macronutrients: carbohydrates, protein, and fat. Each is broken down into its component form (glucose, amino acids, and fatty acids respectively) and used to fuel different processes at different intensities.
Fat provides the most energy per gram – nine calories, compared to four for both protein and carbohydrate. But fat is not the body’s preferred fuel source. That distinction belongs to carbohydrate, particularly at high exercise intensities, where glucose is the most efficient and accessible fuel available. “The theory of doing a high intensity session fasted is very much a myth and actually quite detrimental to energy levels,” says Jenaed.
Water is essential but not a source of energy. And despite what might seem an appealing idea, sunlight provides no meaningful energy for human physiology beyond supporting vitamin D synthesis.
What happens when we don’t have enough energy?
When energy going out consistently exceeds energy coming in, the body goes into a form of preservation mode. This has wide-ranging consequences – and most of them are not immediately obvious.
Jenaed outlines the key effects of energy deficiency in active people:
- Impaired growth and tissue repair – the body cannot rebuild what training breaks down
- Increased injury risk – including stress fractures, which occur when bone repair falls behind bone stress
- Hormonal disruption in females – missed or irregular menstrual cycles, as the body deprioritises reproduction in favour of survival
- Weakened immune function – insufficient nutrients to maintain immune defences
- Deteriorating bone health – inadequate calcium and vitamin D availability
- Reduced training adaptation – the session essentially becomes wasted; the body cannot generate the adaptations it is training for
This cluster of symptoms is formally recognised as Relative Energy Deficiency in Sport (RED-S) – a condition that affects both male and female athletes across all levels of sport. One of its defining characteristics is that it often goes unrecognised for a long time: symptoms accumulate gradually and many – fatigue, lower mood, performance plateaus – are easily attributed to other causes.
Who is most at risk?
Certain groups are at significantly higher risk of energy deficiency, and Jenaed is clear that this is not simply about people who are dieting. The populations she sees most frequently include:
- People with eating disorders or disordered eating – including those with orthorexia (an obsessive focus on “healthy” eating) and those who over-exercise as part of a restrictive pattern
- Adolescent female athletes – under significant social pressure around weight, training hard, and often unaware of how much they actually need to eat
- Older adults – reduced appetite, altered taste, and difficulty swallowing can all reduce intake below requirements
- People recovering from injury – one of the most common and counterintuitive risk scenarios: when injured athletes can’t train, they often cut back on food, not realising that tissue repair significantly increases their energy needs
- Pregnant and lactating women – energy requirements are meaningfully higher and not always met
Dr Seth adds the clinical observation that many patients presenting with injuries turn out to be energy deficient without any awareness of it. The connection between what they’re eating and the injury they’re dealing with is rarely something they’ve considered.
The carbohydrate question
“Everyone loves to hate the carb,” says Jenaed – and she has seen the consequences of that in clinic. Carbohydrate is the body’s preferred fuel source for exercise, particularly at higher intensities. Restricting it in the context of active training is not a neutral choice; it means either underperforming or forcing the body to use less efficient fuel sources.
The exception is weight-category sports, where some athletes may use short-term carbohydrate reduction to make weight. But Jenaed is clear: this is a highly specific, closely managed intervention, not a general lifestyle recommendation. Boxers making weight will tell you exactly how they feel during that phase. It is not a model to emulate.
Low carbohydrate eating can still provide adequate total calories, but it will not support optimal performance in high-intensity sport, and it does not need to be the default for the vast majority of active people.
Practical fuelling: what it looks like
The plate model
For moderate intensity training, Jenaed recommends building meals around the following proportions:
- One third carbohydrate – pasta, rice, quinoa, bread, legumes
- One third protein – meat, fish, eggs, dairy, pulses
- One third vegetables – plus a small amount of healthy fat (avocado, oils, nuts, seeds)
For higher training loads or twice-daily sessions, the carbohydrate proportion should increase – up to half the plate. The body’s needs change with its demands.
Fuelling around exercise
- Before training: a quick-release carbohydrate snack – fruit, fruit juice, or a simple carbohydrate – particularly for sessions lasting over 45 minutes at high intensity
- During training: for sessions over an hour, a carbohydrate solution drink with electrolytes maintains fuel availability
- After training: carbohydrate and protein together – at a ratio of approximately 3:1. Chocolate milk is a frequently recommended and well-evidenced option for post-training recovery
General habits
- Don’t skip meals – the hunger cycle runs on a two-to-four hour rhythm, and gaps larger than that work against energy regulation
- Include two snacks daily – particularly when training volume is high. Three meals a day is often not enough for active people
- Stay hydrated – but don’t confuse hydration with fuelling; water supports physiology but does not replace food energy
- Don’t fear rest days – the body recovers, repairs, and adapts on rest days. Fuelling them appropriately is as important as fuelling training days
- Recognise when restriction is a problem – and seek professional support if eating patterns feel difficult to change
The bottom line
Energy deficiency in sport is common, underdiagnosed, and frequently self-inflicted without any awareness. The consequences range from reduced training adaptation – essentially wasted sessions – through to serious health effects including stress fractures, hormonal disruption, and compromised immune function.
The solution is not complicated in principle: eat enough, eat regularly, fuel around exercise, and stop treating carbohydrate as the enemy. “Food is your toolkit,” as Jenaed puts it. The right tools make the job possible. Without them, the body does the best it can with what it has – and the gaps show up, eventually, as injury, fatigue, or stalled progress.
If you are unsure whether your nutrition is keeping pace with your training, a consultation with a registered sports dietitian is the most effective way to find out.
Jenaed Ruddock is a Registered Sports Dietitian, HCPC and SENR registered, and founder of Nutrition & Co. She specialises in sports performance nutrition, RED-S, and eating disorders in athletes, and works with clients including Cambridge University athletes, Olympic-pathway athletes, and high-performing professionals. She offers individual consultations online and in person.
Find out more at nutritionandco.co.uk or follow her on Instagram at @jenaedruddock.rd
To book an appointment with the LBSM team, visit lbsm.co.uk/booking
Listen to the full episode below ↓
