For Professionals
Working Alongside You, Not Instead of You
I work with people whose symptoms have persisted despite multiple plans, tests and clinicians. If that describes someone on your list, or someone whose needs sit outside your own scope, this page explains how we might work together.
Who I am
A Scientist First
I’m Leah de Souza-Thomas, a functional medicine practitioner and nutritional therapist, and the founder of The Thrive Practice.
I came to practice through public health. I’m registered with the UK Public Health Register, I hold a BSc in Biomedical Sciences, an MSc in Modern Epidemiology and an MPH, and I’ve spent over twenty years working across health protection, health improvement and healthcare public health at local, regional and national level. I trained with the Institute for Functional Medicine and hold a Graduate Diploma from the Institute for Optimum Nutrition.
That background shapes how I practise. I read the primary literature, I’m careful about what the evidence does and doesn’t support, and I’m comfortable saying when something is uncertain. I don’t overstate what nutrition and lifestyle work can do, and I don’t work outside my scope.
You can also find me on LinkedIn.
Training
Where My Training Comes From
BSc (Hons) Biomedical Sciences, University of North London
A comprehensive foundation in human biology, disease mechanisms, and diagnostic science, providing the scientific basis for my functional health work.
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MSc Modern Epidemiology, Imperial College London
Advanced training in analysing disease patterns and prevention strategies, allowing me to apply data-driven insights to individual practice.
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MPH Masters in Public Health, Kings College London
Expertise in public health systems, preventive healthcare, and population health management, which supports my holistic approach to individualised care.
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Institute for Functional Medicine (IFM) Certifications, IFM
I have completed several advanced practice modules through the Institute for Functional Medicine, which equips me with the tools to address complex health challenges through a functional approach:
- Environmental Health: Assessing and mitigating environmental factors that affect health.
- Bioenergetics: Understanding energy systems in the body to optimise health.
- Gastrointestinal Health: Supporting people with digestive symptoms, including IBS and functional gut disturbance.
- Hormone Health: Supporting clients through hormone-related challenges, including PMS and menopause.
- Immune Health: Addressing immune dysfunction and supporting immune resilience.
- Cardiometabolic Health: Supporting blood sugar regulation and cardiovascular health through nutrition and lifestyle.
- Applying Functional Medicine to Clinical Practice: Emphasising personalised, root-cause approaches for tailored diet and lifestyle recommendations.
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GDip Graduate Diploma in Integrative Functional Nutrition, ION
Focused on personalised nutrition, applying integrative approaches to personalised nutrition.
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Functional Nutrition & Lifestyle Training, IFM
- Therapeutic Food Plans: For supporting long-term health.
- Intermittent Fasting: Therapeutic Mechanisms and Clinical Applications: Understanding the evidence for fasting and its clinical applications.
- Potential Micronutrient Deficiencies Associated with Cardiovascular Drugs: Understanding potential nutrient interactions associated with cardiovascular medications.
- Lifestyle: The Foundations of Functional Medicine Building the foundation of health with lifestyle interventions.
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Who I work with
The Cases that Tend to Come to Me
Most people who reach me have already tried a great deal. Their symptoms have persisted through multiple plans, several rounds of tests, and often a series of clinicians. They’re frequently told that everything looks normal.
I work with men and women on:
Digestive and gut symptoms
Hormonal health, including perimenopause and menopause
Immune resilience and recurrent infections
Fatigue and low energy
Weight that isn't responding to the usual approaches
Blood sugar and cardiometabolic risk factors
There is usually more than one thing happening at once, and rarely a single tidy cause. What I offer is time, a structured assessment, and a sequenced plan that fits the person’s actual life rather than an idealised version of it.
When a referral might help
When to Think of Me
A referral may be useful when:
Investigations have been appropriately completed and nothing requiring medical management has been identified, but the person remains symptomatic
Someone needs sustained nutrition and lifestyle support over months rather than a single appointment
Several systems appear to be interacting and the person needs help making sense of the whole picture
A patient wants to work on modifiable risk factors alongside their existing care
You're a practitioner whose own scope, capacity or specialism doesn't extend to complex, multi-system nutritional work
Scope and safety
How I Stay in My Lane
This matters to me, so I’ll be explicit about it.
I do not diagnose, treat, cure or prevent medical conditions. I work with nutrition, lifestyle and functional assessment.
I do not advise anyone to stop, start or change prescribed medication. That remains with their prescriber.
I screen for red flags and refer onward. If something needs medical attention, the person goes back to their GP or to secondary care, and I say so clearly.
I check for relevant interactions before recommending any supplement, and I'm conservative in what I recommend.
Functional testing is used where it genuinely adds something to the clinical picture, not as a matter of routine.
I hold professional indemnity insurance through Balens and work to the standards of my training.
Where you’d like to remain informed, I’m glad to share a brief summary of my assessment and plan with the person’s consent.
Referrals and collaboration
Let’s talk
If you have someone in mind, or you’d simply like to know more about how I work before referring, do get in touch. I’m always glad to have a conversation first.