Dr Nicola Davies, author of ‘I Can Beat Obesity!’, considers the relationship between the two conditions.
It is thought that around one in four adults in the UK are obese (the highest prevalence in Europe at 24.9%).1 In addition, the number of people affected by one or more allergies is thought to be more than one in four, with some sources indicating that the numbers could be as high as 45%.2  The prevalence and co-existence of both conditions has led to many studies being conducted into whether or not there is a link between the two; are people who suffer from one or more allergies more likely to be obese, and why? Or is obesity a causal factor in developing an allergy?, and any evidence that might support such a link.

What is the Evidence?
Many studies have been conducted in the areas of obesity and allergies to look at whether there is a cause-and-effect relationship between the two. The association between obesity and conditions such as allergic asthma, eczema, and food allergies is well documented, with links that have been investigated including lifestyle choices and physiological factors (such as immune system diseases or other medical conditions). Allergies considered within these studies are varied, and include atopic conditions (such as eczema, allergic rhinitis, and allergic asthma) and food allergies – although it should be noted that other substances such as drugs, latex, and insect venom can also cause allergic reactions.

  Obesity can in some cases be caused by underlying medical or genetic conditions, but in the majority of cases it is largely caused by environmental factors and lifestyle choices, and can as a result be thought of as a lifestyle disease. Conversely, allergies are largely considered to be caused by a hypersensitive immune system. The link between obesity and allergies, therefore, could be broken down further to consider how lifestyle choices influence the body’s immune system. However, there are of course circumstances in which obesity is not caused by lifestyle, and this also needs to be considered.

Can unhealthy lifestyle choices cause allergies?
If allergies can be caused by obesity, and obesity is brought about by unhealthy lifestyle choices, then can it be said that these choices are at the root of why a person develops a particular allergy?

  Unhealthy lifestyle choices that can cause obesity include low levels of activity and poor diet, with the link between these being well documented. In terms of low levels of physical activity and allergies, there is also evidence to support a link between the two. For example, a global survey, the Avon Longitudinal Study of Parents and Children (ALSPAC), revealed that those who watched television for more than two hours a day had higher risks of allergic asthma.3 This finding is supported by further research conducted by Mitchell et al. (2013), which found evidence to link a sedentary lifestyle with an increased risk of asthma and eczema. 4 In relation to poor diet and allergies, studies have shown that a lack of certain healthy dietary components can also have an adverse effect; antioxidants from fruits and vegetables are beneficial for inflammation and obesity, and data from 137 individuals with allergies has shown that a high oxidant diet can significantly reduce allergy symptoms.5

  Now to consider what can be done to combat obesity with a view to minimising the risk of developing allergic symptoms. Epidemiological evidence suggests that increased weight gain increases the risk for developing autoimmune and atopic conditions,6 so it could be said that it is preferable for overweight and obese individuals to maintain a lifestyle that can result in them reducing their BMI with a view to minimising that risk. Increasing levels of physical activity and eating a healthy diet are key components to helping obese people lose weight, and including specific foods and supplements within a diet can go even further to help minimise allergic symptoms.

  For example, good bacteria such as probiotics can help to keep the gut healthy, and by extension help to keep the body healthy as a whole. Probiotics have been known to treat allergies by boosting both the immune and digestive systems. For instance, a longitudinal study revealed that infants who ingested non-pathogenic E. coli developed fewer allergies when they were tested 10 and 20 years later.7 Furthermore, probiotics are thought to help prevent obesity by moderating appetite and metabolic functions. Probiotics such as fermicutes and bacteriodetes can help to regulate gut bacteria; fermicutes are gut bacteria which cause fermentation of carbohydrates, leading to fat formation, and bacteroidetes produce enzymes that help us get the best nutritive value from the plant cell walls found in fruits and vegetables. Studies have shown that heavier people have more firmicutes and fewer bacteroidetes,8 so by regulating these bacteria, probiotics can help to ensure that levels of bacteria that cause fat formation are minimised.

  In addition, studies have shown that the Mediterranean diet, which is rich in seafood, can result in favourable effects among asthma sufferers.9 The Mediterranean diet also includes eating plenty of fruits and vegetables, which are key components of a healthy diet. It is thought that this diet is beneficial in terms of combating conditions such as asthma due to the nutrients within the diet (including essential fatty acids, fibre and antioxidants) that help fight against oxidative stress.

Physiological/medical factors at play
Lifestyle choices are not always the reason behind a condition such as obesity. Sufferers may be predisposed to certain conditions that cause obesity, allergies, or both. For example, in relation to obesity, hypothyroidism and Cushing’s disease can contribute to weight gain, as can medications such as corticosteroids and antidepressants.10 Prader-Willi syndrome, a rare genetic condition, can also cause weight gain; one of the key characteristics of this condition is hyperphagia (overeating), which needs to be managed carefully in order to maintain a healthy weight.11 However, when considering the link between allergies and obesity, there are many underlying medical components at play, such as immunological conditions like food allergies and hormonal imbalances.

  Hersoug and Linneberg (2007) discuss how atopic diseases, or a hereditary tendency to have an immediate allergic response like allergic rhinitis and atopic eczema, are at least in part caused by a weakened immunological tolerance.6 As white adipose tissue or white fat secretes adipokines, which are circulating hormones that mediate inflammation and insulin resistance, an increase in weight may be connected to more sensitive T-cells or T-lymphocytes. These subtypes of white blood cells are produced by the thymus gland and play an active role in immune responses. Also, Adiponectin, which is a protein involved in regulating fatty acid breakdown and glucose levels, decreases with higher obesity. This suggests that being obese is linked to autoimmune disorders, as there is a connection between decreased tolerance to antigens or foreign substances that may prompt the immune system to produce antibodies.

  Intake of foods that cause an immune system response can also contribute to weight gain. When you take in food to which you are allergic, your adrenal glands produce hormones that negatively affect your insulin and blood sugar levels, thereby prompting your body to store more fat instead of using it for energy. Hence, having food allergies may result in weight gain, which in turn increases inflammation and allergy-related problems.12 This vicious cycle clearly links obesity with allergic diseases.

  Food allergies can also be responsible for bloating, water retention, and slow metabolism. An imbalanced gut flora is associated with both obesity and allergy13 and consuming food to which you are sensitive causes inflammation that activates the adrenal glands to secrete blood-sugar-destabilising hormones. As a result, the body holds on to fat rather than burning it for energy. In addition to this, reactivity to certain foods or food intolerance can result in fluid retention due to immune system cells attempting to “dilute” the effects of these foods14 , resulting in bloating and puffiness. For some people, eliminating foods with yeast, gluten, and dairy, can facilitate weight loss. This can be a challenge, however, since many people crave what they are allergic to.

  Research conducted into levels of certain types of antibodies has also provided insight into the link between appetite and allergies. Immunoglobulin E (IgE) are antibodies that attack allergens, viruses, bacteria, and other antigens. IgE tests have been employed to test allergic reactions to asthma as well as lesser immunity to parasitic infections. One study sought to determine the relationship between IgE levels and obesity through the immunomodulatory effects of Ghrelin and Leptin – the “hunger hormones.”15 Both hormones have been found to occur in higher levels among the obese.16 The data gathered from 98 obese subjects reflected a correlation between weight and pre-allergic symptoms. A strong inverse correlation was also found between Ghrelin and IgE levels, whereby a lower level of Ghrelin was associated with a higher level of IgE and vice versa. This implies that Ghrelin may directly or indirectly constrain the production of IgE, suggesting a link between weight-related and allergy-related hormones.

  The health of a mother can also directly influence a child’s immunity levels and disposition to allergic diseases; maternal obesity is one of the main factors that can impact newborns’ immune system development,17 and infants born to obese mothers have been found to have lower immunity levels as evidenced by fewer antibodies. One study, which appeared in the International Journal of Obesity, has corroborated that there is an apparent inter-relationship between asthma and obesity genes18; specifically, pleiotropic genes or genes that have many influences on a certain set of characteristics are highly assumed to be involved in both obesity and allergic diseases. This finding has prompted further research into whether there is a link between the same genes and allergies.

What can be done?
The evidence does suggest a link between allergies and unhealthy weight gain, and the causes can be thought of in terms of those brought about by lifestyle and those that are physiological in nature (i.e. not caused by lifestyle choices, such as autoimmune conditions). Being obese may cause a domino effect of complications such as allergic disorders and vice versa.

  Population health can be improved by implementing information programmes that inform the public of the link between these two conditions, encouraging people to speak to their physicians and family doctors if they have any concerns about underlying medical conditions, and promoting healthy lifestyle choices to combat obesity. These programmes, which would promote healthy living regimens and exercise-friendly environments, could help to weaken the link between obesity and allergies in cases where the exacerbation of allergic symptoms is being caused by lifestyle-induced obesity. In cases where the allergy or weight gain is caused by an underlying condition that was previously unknown, sufferers can be encouraged to find out more about the causes and hopefully find effective treatments to disrupt the allergy-obesity cycle. In either scenario, there is the potential of providing relief to the vast numbers of the UK population who suffer from one or both conditions. More importantly, such measures could be an important step towards reducing obesity and allergy incidence and prevalence.


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This article first appeared in Allergy Newsletter No. 120. Summer 2017.