The elusivequest for eternal youth may be a myth, but slowing the visible and felt effects of ageing is an achievable goal, according to Harvard-educated physician Dr Ian K Smith.

In his new book, Eat* Your Age*, Dr Smith challenges the notion that vitality is solely dependent on wealth or cosmetic procedures, instead emphasising mindful planning and a deep understanding of one’s body.

"There’s so much you can do to keep yourself looking and feeling youthful, and it doesn’t depend on how much money you have or how many times you visit the plastic surgeon," Dr Smith states.

"It’s about how well you plan, how aware you are of your body and health, and the simple steps you can take to forge a path of vigour and vitality that has nothing to do with the number of candles on your birthday cake."

Dr Smith’s approach is built on the premise that our nutritional, metabolic, and medical requirements evolve with age, necessitating a corresponding shift in our eating habits. Rather than offering a one-size-fits-all diet, his book guides readers on how to align food choices, physical activity, and preventive care with the specific demands of each decade of life.

The ultimate goal, he explains, is to "help slow metabolic decline, preserve muscle, reduce chronic disease risk, and extend health span – not just lifespan." He aims to empower individuals to "take control of ageing through practical, science-based strategies that make longevity an intentional, achievable process."

Revealing youthful secrets: Dr Ian K Smith (Triste Smith/PA)

Here, Dr Smith outlines key dietary, movement, and health measures for specific decades to foster a younger look and feel.

Your 30s: Choices that shape future health

The choices made in your 30s quietly begin to shape how you age. While the body remains resilient, "early metabolic shifts are already underway, making prevention far more powerful than correction," Dr Smith explains. This decade is crucial for building strong nutritional habits, consistent movement patterns, and medical awareness that will yield long-term benefits.

For nutrition, Dr Smith advises a shift from purely calorie-focused thinking to nutrient density, prioritising lean protein at every meal, fibre-rich vegetables, and healthy fats, while minimising ultra-processed foods.

"This decade is about preventing insulin resistance before it starts," he says, noting that subtle changes in blood sugar, cholesterol, and inflammatory markers can begin without obvious symptoms. Balanced meals combining protein, fibre, and healthy fats are essential for slowing digestion, reducing blood sugar spikes, and sustaining energy. He warns that relying heavily on refined carbohydrates or skipping meals can set the stage for metabolic dysfunction later.

Foods such as salmon, broccoli and blueberries are rich in antioxidants (Alamy/PA)

In terms of movement, establishing a consistent resistance-training routine (at least two to three days per week) is vital. "Muscle mass gained in your 30s becomes metabolic insurance later in life," Dr Smith explains, adding that strength training improves insulin sensitivity, protects joints, and raises resting metabolic rate.

This should be paired with moderate cardiovascular activity, such as brisk walking, cycling, or swimming, to support heart health without excessive stress.

Medically, baseline lab tests are recommended, including fasting glucose, lipid panel, blood pressure, and waist circumference. These markers "create a personal health starting line and help identify silent risks early."

Your 40s: Strategic maintenance and metabolic protection

The 40s mark a transition from building health to actively protecting it. Hormonal changes and a gradual metabolic slowdown mean the body no longer responds as it once did, even if habits remain unchanged. "This decade calls for smarter nutrition, more intentional exercise, and proactive screening to stay ahead of silent risks," Dr Smith advises.

Nutrition to support hormonal shifts becomes paramount. As the metabolic rate slows, protein is essential for preserving lean mass and managing appetite. Hormonal fluctuations, particularly in oestrogen, testosterone, and cortisol, begin to influence fat storage and stress response. "It’s important to spread protein evenly across meals rather than concentrating it at dinner," Dr Smith stresses, as this supports muscle repair, stabilises blood sugar, and reduces late-night overeating. Paying attention to portion sizes and reducing liquid calories also becomes increasingly important, as caloric needs decline even if hunger persists.

Medically, baseline lab tests are recommended, including fasting glucose, lipid panel, blood pressure, and waist circumference (Alamy/PA)

To maintain cardiovascular fitness, Dr Smith suggests incorporating higher-intensity workouts alongside strength training. Short bursts of interval training can help maintain fitness and counter age-related metabolic slowdown. Recovery is also crucial: "Adequate sleep, mobility work, and rest days are essential to avoid burnout and injury."

Medical screening in your 40s should include discussions for routine bowel cancer screening, and regular monitoring of blood pressure, cholesterol, and diabetes, especially if there is a family history.

Your 50s: Preserving strength, reducing inflammation

In your 50s, health becomes less about weight and more about resilience, Dr Smith notes. Muscle loss, inflammation, and chronic disease risk accelerate unless directly addressed through diet and movement. "The goal of this decade is to preserve strength, protect joints and bones, and maintain metabolic stability."

For nutrition, adopting a more anti-inflammatory eating pattern is key, emphasising omega-3 fats, colourful vegetables, whole grains, and reduced added sugars. Digestive efficiency and insulin sensitivity often decline in the 50s, making food quality more important than quantity. "Inflammation – not ageing itself – is a major driver of chronic disease," he warns. Foods rich in antioxidants help protect blood vessels, joints, and the brain. Adequate protein remains critical, as does hydration, given that thirst signals can weaken with age. Mindful eating and slower meal pacing also improve digestion and nutrient absorption.

Omega-3 fats, colourful vegetables, whole grains, and reduced added sugars are key for nutrition (Alamy/PA)

Movement in this decade requires making strength training "non-negotiable," while adding balance, mobility work, and exercises that challenge stability, such as single-leg movements. "Muscle loss accelerates during this decade if not actively resisted," he cautions.

Medically, scheduling bone density testing and screenings for cardiovascular disease, diabetes, and cancer is vital, as "early detection dramatically improves outcomes."

Your 60s and beyond: Sustaining independence and quality of life

The focus in your 60s and beyond shifts from optimisation to preservation and targeted growth. Daily habits now determine mobility, cognitive health, and independence more than numbers on a scale. "Eating well, moving consistently, and staying medically vigilant become the foundation for a longer, more vibrant life."

Specific nutrient needs include adequate protein, calcium, vitamin D, and hydration, while moderating total calories. "Appetite may decline, but nutrient needs remain high," Dr Smith says, highlighting that under-eating protein is a "common and dangerous mistake" in older adults. Protein supports muscle strength, immune function, and recovery from illness. Meals should be "simple, nutrient-dense, and easy to digest."

Eat Your Age cover (HQ/PA)

To stay mobile and reduce the risk of falls, prioritise functional movement – strength, balance, flexibility, and walking. "The goal isn’t intensity, but consistency and safety," Dr Smith explains. Regular movement preserves mobility, reduces fall risk, and supports brain health, with even short daily sessions making a meaningful difference.

Medically, maintaining consistent vision, hearing, cognitive, cardiovascular, and medication reviews is crucial. "These screenings protect quality of life and help preserve independence well into later years," Dr Smith concludes.

Eat Your Age** by Dr Ian K Smith is published by HQ, priced £10.99. Available now.**