How to feed your teen: With Vanessa McNamara and Karlein Duvenage
- Dr Natalie Hutchins
- Nov 12
- 5 min read
Guest bios:
Karlien Duvenage is a registered dietitian and nutritionist based in Singapore. She also holds a Master’s degree in Psychology. With nearly 20 years’ experience in sports and exercise nutrition, gut health, eating disorders, and family wellness. She combines evidence-based practice with a compassionate, psychologically informed approach. She has worked with Olympic-level athletes, as well as active individuals across all ages and abilities. Her recent training spans trauma-informed care, inclusive feeding support, and family-based eating disorder treatment, helping clients of all ages rebuild a positive, confident relationship with food.
Vanessa McNamara is a clinical dietitian with over 25 years’ experience across hospitals, community settings and private practice. She works with children of all ages on issues ranging from selective eating, food allergies, and gastrointestinal conditions to growth concerns and eating or feeding disorders. Vanessa has a special interest in supporting picky eaters and children with sensory-based feeding challenges, helping them build positive relationships with food. She is Co-Chair of the Eating Disorder Interest Group of the Singapore Nutrition and Dietetics Association, serves on the Executive Committee of the Asthma and Allergy Association, and is a member of SNDA and Dietitians Australia.
In this episode, we cover:
Why adolescence is the second biggest growth phase after infancy and what that means for nutrition
How to avoid the “Goldilocks trap” of being too controlling or too hands-off around food
Language to use (and avoid) when talking about eating and body image
Common nutrient deficiencies in teens especially iron and calcium
How to support vegetarian or vegan teens safely
Practical tips for fuelling teen athletes (without falling for supplement marketing)
What relative energy deficiency in sport (RED-S) is and why losing a period isn’t “normal” for athletic girls
Early red flags for eating disorders and how to respond supportively
Gut health myths: microbiome testing, probiotics, and the truth about “detox” diets
Food allergy vs. intolerance testing what’s actually evidence-based
The difference between a dietitian and a nutritionist
Key Takeaways
1. Teen nutrition: not just “adult rules, smaller portions”
Teens often need as much or more energy than adults, especially if they’re active. Adolescence is also a critical window for long-term cardiometabolic and skeletal health. Patterns established now track into adult risk for obesity, cardiovascular disease, type 2 diabetes and osteoporosis.
Vanessa and Karlein walk through:
Why regular eating protective: better concentration, mood, training performance and appetite regulation.
The risk of applying adult wellness trends to still-growing bodies.
2. Iron & calcium: the quiet crisis nutrients
Iron: Iron needs jump with the growth spurt and menstruation. In some recent data, up to ~35–40% of 12–21-year-old females meet criteria for iron deficiency. Add heavy periods, low red meat intake, skipped meals, and poorly planned vegetarian/vegan diets, and it’s easy to miss. The trio discuss:
Possible symptoms of iron deficiency
Why vegetarian or vegan teens can meet needs but only with deliberate inclusion of iron-rich foods (pulses, tofu, nuts, seeds, fortified foods, leafy greens) plus vitamin C to enhance absorption, and targeted testing when in doubt.
Calcium & bone health: Up to 90% of peak bone mass is laid down by the end of adolescence; recommended calcium intakes are ~1300 mg/day for ages 9–18 (vs 1000 mg for most adults). Undershooting here, especially in sporty girls, dairy-free teens, or those with restrictive eating, can set up lower bone density and fracture risk later on.
3. Autonomy vs oversight: finding the “Goldilocks zone”
Parents are often stuck between:
Over-control: food policing, weight-commentary, “good/bad” foods — linked in the literature to higher disordered eating risk and body dissatisfaction.
Over-permissive: no structure, no shared meals, no support with choices.
Vanessa and Karlein offer a middle ground:
Keep structure (predictable meals, snacks, family eating where possible).
Offer variety and choice within that structure.
Ditch moral language (“junk”, “naughty”, “clean”) and talk about what foods do (energy, focus, strength, enjoyment) rather than their virtue.
Pause and examine your own history with weight, dieting and body shame before reacting to your teen’s body or plate.
4. Picky eating, sensory needs & neurodivergence
Picky eating doesn’t magically disappear by the teen years for all children. For some teens, especially those who are neurodivergent, sensory-sensitive, or living with gut issues, it persists and is not “bad behaviour”.
Karlein and Vanessa explain:
How sensory profiles and GI discomfort drive avoidance.
Why forcing, bribing or shaming backfires.
The value of family-style meals with at least one “safe” food, low-pressure exposure, and teen involvement in choosing realistic next steps.
Where intake is very limited, growth is affected, or anxiety around food is high, they recommend early input from a dietitian and, if needed, occupational therapist or psychologist.
5. Fuelling teen athletes (and why a missing period is not a badge of honour)
For sporty teens, the foundations are the same, just more of everything:
Well-timed carbs and protein around training,
Hydration (sports drinks selectively, not as a lifestyle accessory),
Practical strategies for long school/sport days and hot climates.
They unpack Relative Energy Deficiency in Sport (RED-S) and the Female Athlete Triad:
Low energy availability (not eating enough for training + growth),
Menstrual disturbance,
Impaired bone health.
Supplements like protein powders, creatine and “pre-workouts” are discussed with caution: food first, targeted use only when genuinely indicated, and always considering contamination risk, unrealistic body ideals and the worrying link between early supplement use and later steroid use in some studies.
6. Eating disorders & red flags: when to worry sooner, not later
Many early signs may be disguised as “healthy choices”:
Sudden cutting of food groups (carbs, fats, meat, dairy) without medical reason.
Rules, rituals, micro-portioning, distress if foods are “wrong.”
Cooking for others but not eating; only trusting food they prepare.
Withdrawing from family meals; body-checking; escalating exercise.
Increasing rigidity framed as “wellness,” “clean,” “plant-based,” or “being disciplined.”
Early, proactive intervention for suspected eating disorders in young people is key. This leads to better outcomes, lower admission rates, and less entrenched patterns when treatment starts early.
Vanessa outlines the dietitian’s role within a multidisciplinary team (GP/paediatrics, psychiatry, psychology): restoring medical safety, normalising regular eating, rebuilding trust in food, and supporting parents to lead refeeding when needed.
7. Body image, language & modelling
The conversation closes with a theme that runs through the whole episode: our kids are watching us.
Evidence links parental comments about weight and dieting, even well-meant, with increased body dissatisfaction and disordered eating in young people.
Practical shifts:
Speak about bodies with respect and gratitude (“strong”, “capable”, “helps me do…”), not size.
Don’t critique your own body or others’ in front of your teen.
Keep food talk neutral and curious, not moral or fearful.
Recommended Reading (TWH Book Club)
How to Raise an Intuitive Eater — Sumner Brooks & Amy Severson
Feeding Families — Jill Castle
Extra resources
Karlein’s basic sports drink recipe is:
To Make 1 L
o 250ml 100% Fruit juice (choose your child's favourite)
o 750ml water
o 2 tbsp sugar
o Pinch of salt
o Mix until everything is dissolved.
References:
Weyand AC, Chaitoff A, Freed GL, Sholzberg M, Choi SW, McGann PT. Prevalence of Iron Deficiency and Iron-Deficiency Anemia in US Females Aged 12-21 Years, 2003-2020.
JAMA. 2023;329(24):2191–2193. doi:10.1001/jama.2023.8020
Eating disorders: recognition and treatment. NICE guideline, Published: 23 May 2017
