Breathlessness on exertion is a common symptom in people with obesity. It can have several coexisting causes, so we ask how it developed and what tests have already been done, including patients who do not mention breathlessness themselves. This part describes breathlessness that has lasted for weeks or months. Sudden or rapidly worsening breathlessness requires immediate medical help.
What causes breathlessness in someone with healthy lungs?
Fat around the abdomen and chest pushes the diaphragm upwards, reduces the amount of air left in the lungs after a normal breath out and increases the work the breathing muscles do with every breath. A study of 373 people with normal airway patency measured how lung volumes change with BMI. In this group, at a BMI of 30 the amount of air remaining in the lungs after a normal breath out was 75 percent, and the amount that could still be breathed out was 47 percent, of the values seen in people with a BMI of 20. The largest changes occurred already with overweight and class I obesity. Other lung volumes remained within the normal range on average, which is why spirometry can be normal in a person with marked breathlessness. The results describe a relationship in the study group and do not predict the result for every person with a given BMI. In a meta-analysis of seven studies involving more than 333,000 adults, overweight and obesity were associated with more frequent development of asthma in both sexes, and the association was stronger with obesity.
How is the cause of breathlessness determined?
Investigations are guided by the medical history and examination. Spirometry with a bronchodilator test helps detect airflow problems, but a single normal result does not rule out asthma or every cause of breathlessness. The doctor may recommend repeating spirometry, home peak expiratory flow (PEF) measurements or other tests. The table below organises the questions we ask during the appointment. It helps the conversation with the doctor and is not a tool for self-diagnosis.
| Symptom or test | Asthma | COPD | Effect of body weight |
|---|
When breathlessness occurs | Often in episodes, including at night and early morning | Builds up gradually, first on exertion | On exertion |
Wheezing | Common on breathing out, but its absence does not rule out asthma | May be present | Usually absent |
Cough | Often dry and in bouts, e.g. after cold air | Long-lasting, often with phlegm | Usually rare |
Response to a bronchodilator | Often clear relief, but this alone does not confirm the diagnosis | Varies and does not reliably distinguish COPD from asthma | Slight |
Spirometry result | Variable airway narrowing, often improving after the medicine | Airway narrowing that persists after the medicine | Often normal |
After weight loss | Disease control may improve | The plan depends on nutrition and muscle | May ease |
A Canadian study assessed 496 adults whose asthma had previously been diagnosed by a doctor. After serial diagnostic assessment, with medicines withdrawn under medical supervision, asthma was not confirmed in 31.8 percent of people with obesity and 28.7 percent of people without obesity. Of those in whom asthma was ruled out, 65.5 percent needed no medicines or appointments for breathlessness during the following six months of observation. Obesity did not increase the risk of misdiagnosis, as the proportions in both groups were similar. A doctor can therefore review an asthma diagnosis made in the past without tests, but patients should not stop their inhalers on their own.
What does weight loss change for a person with asthma?
One randomised trial, from Finland, included 38 people with asthma and a BMI of 30 to 42. The weight-loss group followed a supervised very low-calorie diet, faster than the pace we suggest to our patients. After a programme that included an eight-week diet, weight in this group was 14.5 percent lower, compared with 0.3 percent in the control group. After one year, the first group weighed 11.3 percent less than at baseline and the second 2.2 percent more. Forced expiratory volume in one second (FEV1), the amount of air breathed out in the first second and the basic measure of airway patency, changed more favourably in the weight-loss group than in the control group. The difference in change between the groups was 7.2 percentage points of the predicted value at the end of the programme and 7.6 points after one year, and 8.6 points for vital capacity at the end of the programme. A separate analysis looked at data from 3,073 adults with moderate asthma from four trials of disease-controlling medicines. In this post hoc analysis, the higher the BMI, the weaker the response to an inhaled corticosteroid, while the response to montelukast remained similar. The finding comes from re-analysing data collected for another purpose and is not a reason to switch an inhaled medicine.
Data on surgical treatment come from observational studies. A review of 33 studies involving 3,731 people with asthma after bariatric surgery reported that 47 percent stopped their asthma medicines, remission of asthma was recorded in 58 percent, and FEV1 and vital capacity increased by 8 to 9 percentage points. Remission in such studies does not mean a lasting cure, and the results are not guidance for stopping medicines. In observational studies, people taking GLP-1 analogues had fewer asthma exacerbations, but other factors may have influenced this result. The effectiveness of these medicines in treating asthma needs to be confirmed in randomised trials. Patients do not change their inhaler doses themselves, and any change is decided by the doctor treating their asthma after reassessing disease control.
How much weight is gained after quitting smoking, and what do we do about it?
A review of 62 studies found that people who stopped smoking without medication weighed on average 1.1 kg more after one month, 2.9 kg more after three months, 4.2 kg more after six months and 4.7 kg more after one year. Individual results varied widely: after one year, 16 percent weighed less than on the day they quit, 37 percent had gained less than 5 kg, 34 percent between 5 and 10 kg and 13 percent more than 10 kg. In a study of more than three thousand people followed for an average of a quarter of a century, those who had stopped smoking in the previous four years gained a median of 2.7 kg over that period if they did not have diabetes and 3.6 kg if they did. Despite the weight gain, they had fewer cardiovascular events than people who continued to smoke. In people without diabetes the finding was statistically stronger, while in people with diabetes the estimates were less precise. The benefits of not smoking outweigh the effects of weight gain.
We plan weight management alongside support for staying smoke-free. For some people, the first goal is to limit weight gain. We explain this at the initial consultation so that the patient does not see a stable weight as a failure. Dietitian support with meal planning can be sought separately; it is not included in the programme. The doctor matches the pace of weight loss and any medication to the patient's health, with no mandatory waiting period after stopping smoking.