Can cutting sugar lower blood pressure in 10 days?
We give the BHF perspective on news stories about the effect of cutting sugar in the diet on blood pressure and other measures of health.
The BHF’s view:
The study was published in Obesity on 28 October 2015 and was led by Dr Robert Lustig at the University of California. It was based on 27 Latino and 16 African American obese children aged between 8 to 18 years, who have at least one other health issue such as high blood pressure. The children chosen for the study regularly consumed high volumes of sugar (over 15 per cent of dietary intake).
Obesity leads to high levels of glucose in the blood. Over time, this can increase the risk of cardiovascular disease such as coronary heart disease, a condition where atheroma (or fatty materials) accumulates in artery walls restricting the flow of blood to the heart. People who are obese are also more likely to develop type 2 diabetes and high blood pressure, which also increase the risk of heart attacks and stroke.
The researchers wanted to find out whether reducing sugar intake can improve cardiovascular health in children.
Cutting sugar reduces blood pressure
During the nine-day study, sugar content of all participants’ diets was reduced from 28 per cent to 10 per cent. They were given starchy foods instead, such as bagels, cereal and pasta, so that they consumed the same amount of calories as they had done previously – the intention was to keep their weights the same. They were still allowed unhealthy foods like crisps and supermarket pizza.
The authors found that diastolic blood pressure (the lowest measure of pressure which occurs when your heart is relaxing between beats) decreased by five mmHg and levels of blood cholesterol decreased by 46 per cent. They also found a marked improvement in glucose tolerance.
Dr Lustig and his fellow authors suggest their findings support a new and exciting direction of research around the negative effects of sugar. The authors said: “Concerns surrounding the role of sugar consumption in chronic disease have previously focused on its caloric equivalence and its role in fomenting increases in weight. This study argues that the health detriments of sugar are independent of its caloric value or effects on weight.”
Both adults and children on average are exceeding their recommended daily sugar intake so it’s important we continue to work as hard as we can to change our behaviour.
BHF Heart Health Dietitian
However, there are some limitations to the study. During the study it was not possible to keep the children’s weights exactly the same, and some children did lose weight. Also, the participant’s normal calorie intake was based on their own estimation, which is usually under-estimated, so some of the results seen could have been the results of calorie reduction.
The absence of a control group (a group studied in the same way but who did not make the changes that were being tested) is also a limitation. This is a feature of the best-designed studies, which makes it easier to be sure that the change being looked at is what is causing the effect. Instead, the researchers only compared the children with how they had been previously.
The study was only based on a small and very specific group – Latino and African-American children who were obese and had another health issue. So we don’t know whether these findings would apply to the general population. Studying a larger group would also increase the reliability of the findings.
How the study was reported
This study was covered by the Daily Express, amongst others, which said: “The key fact in this ground-breaking research appears to be that we can still enjoy high-calorie foods, providing we reduce the sugar content in our overall diets.”
But the study does not prove this. What it did show is that reducing sugar may have health benefits even if weight is not reduced. But that doesn’t mean that losing weight would not have benefited the children even more, as the study did not look at this. Eating a balanced diet and keeping to a healthy weight remains the best advice.
The Express headline “Quickest way to lower blood pressure” is not substantiated by the study, because it didn’t compare different ways of lowering blood pressure (such as exercise or losing weight) and also the study findings may not apply to the general population.
Tracy Parker, BHF Heart Health Dietitian, said: “This study is interesting, but we need more research to confirm these findings. Previous studies have suggested that eating too much added sugar increases a person’s risk of development of diseases, including cardiovascular disease, type 2 diabetes, hypertension and high cholesterol, because of the link with excess calorie intake leading to obesity. However, this small and short-term study found that removing added sugar from the diets of already obese Latino and African American children improved their metabolic health, without changing weight.
“Both adults and children on average are exceeding their recommended daily sugar intake so it’s important we continue to work as hard as we can to change our behaviour. Replace sugary drinks with water or sugar-free versions and instead of sweets, biscuits and chocolate, try healthier alternatives like fresh fruit and vegetables, unsalted nuts and seeds and plain popcorn.”