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Dr Colin

Answering all your Health and Immunity concerns

Dr Colin Hamilton-Davies, our health and immunity specialist, is here to answer your questions on all aspects of immunity and health.

Dr Colin Hamilton-Davies

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Does my weight impair my body’s ability to fight off diseases? I am particularly concerned that being overweight might increase my risk of developing severe symptoms from COVID-19 infection.

The question I am addressing this week takes us to the heart of one of the greatest challenges facing us as a country. No, this has got nothing to do with politics or the economy. It has everything to do with the body, and moreover with being overweight and obesity – the creeping epidemic affecting around 67% of adults in the UK.

This figure has likely increased with the changes brought about by the pandemic. With over half of the UK’s workforce having transitioned to home or flexible working, many people are beginning to feel the effects of poorer eating and lifestyle habits.

To get straight to the point, there are important connections between your body weight and the health of your immune system. It’s much harder for your body to fight off infection when you have a higher percentage of body fat. Obesity in particular places pressure on our bodies, making us more vulnerable to many diseases, such as high blood pressure, high cholesterol, cancer, diabetes and cardiovascular problems. So, weight management should form part of anyone’s long-term strategy for supporting their immune system.

Obesity and COVID-19

Paying attention to your body weight is particularly important within the context of the COVID-19 pandemic. A number of studies have investigated the links between BMI (Body Mass Index) and risk of admission to intensive care from COVID-19, revealing the situation we currently face.

A BMI of 25 or above increases your risk of admission to intensive care by 50%. A BMI of 35-40 increases the risk of dying from COVID-19 by over 40%, and with a BMI greater than 40 by 90%. One recent study has found that obesity and chronic disease are important risk factors for in-hospital mortality in younger age groups specifically (meaning people under 50 years of age).

If you are wanting to do something about your weight, then there is no better time to do this than now. Perhaps start by calculating your BMI and seeing where you fit in relation to the above risks.

The science of fat

The science behind fat build-up in the body and the weakening of immune response is fairly straightforward, although frequently misunderstood. Having a high percentage of body fat has the effect of impairing your immune function, which means that it’s harder to fight off an infection.

There are two types of fat in the body, brown fat and white fat. White adipose tissue has been shown to secret pro-inflammatory cytokines, which over a long period of time induce a state of chronic inflammation. What this means is that your immune response to any new infection may be severely compromised.

Being overweight also importantly affects your responsiveness to vaccinations. It’s been shown in hepatitis B vaccination in healthcare workers, that those workers who are overweight show a higher degree of non-responsiveness to the vaccine. The connections between weight and COVID-19 vaccination are yet to be fully understood, although some studies have suggested that being overweight might indeed lower vaccination efficacy. There is as yet no consensus on this though.


The links between weight gain and diabetes are further cause for concern. Almost 4 million people in the UK have been diagnosed with diabetes, with 90% having type 2 Diabetes, which is linked to obesity and diet, and a further 12 million people being at risk of developing diabetes. The links between diabetes and higher risk of developing severe COVID-19 symptoms are by now well known.

The main culprit for type 2 diabetes is overconsumption of ultra-processed food and drink. These are packaged products with 5 or more ingredients usually containing sugar, unhealthy oils or fats, salt, and ultimately lacking in fibre, vitamins and minerals. These types of food make up an estimated 50% of calories consumed in the UK. Consuming ultra-processed food and drink increases chronic inflammation, severely undermining your immune system and your body’s ability to fight off infection.

Maintaining a healthy diet

The NHS Eatwell Guide provides advice for achieving a healthy, balanced diet.

The good news is that type 2 diabetes may be reversed by maintaining a healthy diet and undertaking a responsible weight management plan – remember to consult with your doctor or GP before undertaking any change to your eating or exercise routine.

In my previous blog post on whether supplements can boost your immune system, I provided a brief outline of what a balanced plate should look like. This is worth repeating. In general, your meals should consist of:

  • 50% carbohydrates, including fruit and vegetables;
  • 25% wholegrains and fibre found in nuts, brown rice, oats and whole-wheat flour;
  • 25% good-quality protein sources.

Remember to try and eat some protein with every meal, and to cut processed food to a minimum. Make sure you are consuming as little sugar as possible. If you are unsure about the nutrient content of a food product, just check the label. You should also try to eat whole foods where possible, including whole fruit and non-starchy vegetables (such as green beans, spinach and broccoli); pulses such as peas, beans and lentils; whole grains; fish; and especially oily nuts and seeds. This follows along the lines of a Mediterranean-style diet.

Your overall fat intake should not consist of more than 20% of total food intake, and not more than a third of this should consist of saturated fat.

There is much information on maintaining a healthy diet and nutrition available on the internet. However, the bottom line when it comes to weight management and immunity remains the same: being overweight or obese impairs your body’s ability to fight off diseases, and can be an important risk factor for hospitalisation and admission to intensive care with regards to COVID-19 infection.

So, manage your weight carefully, eat healthily, and give your immune system the support it needs.

Colin Hamilton-Davies

Dr Colin has over 30 years of experience working as an intensive care specialist.
He’s the Clinical Lead for the Acute Cardiac Critical Care Department at St Bartholomew’s Hospital, City of London, one of the largest critical care units in the UK. He is also Clinical Associate Professor at University College London, where he has been involved in research on the immune system for the past 25 years. Dr Colin is passionate about health & wellbeing and helping people proactively improve their immunity and health.

“Over the coming weeks, Dr Colin in collaboration with Thrive4Life, will be providing you with practical advice on various aspects of immunity and health.”

Ask Dr Colin

If you have a question regarding protecting your immunity then use this contact form to ask Dr Colin any questions you might have.
Dr Colin will attempt to incorporate an (anonymised) response to you in his weekly blog.

    Dr Colin’s responses are intended for informational and educational purposes only and do not constitute medical advice. If you intend on making any change to your diet, lifestyle or exercise routine based on the information provided, make sure to consult your GP or medical professional first to discuss any health concerns. Neither Dr Colin nor Thrive4Life are liable for any issues associated with using or acting on the information on our blog.
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