COVID-19 and metabolic syndrome: could diet be the key?

Editorial EBM Journal

In the current COVID-19 pandemic, governments mandate social distancing and good hand hygiene, but little attention is paid to the potential impact of diet on health outcomes. Poor diet is the most significant contributor to the burden of chronic, lifestyle-related diseases like obesity, type 2 diabetes and cardiovascular disease.1 As of 30 May 2020, the Centers for Disease Control and Prevention reported that among COVID-19 cases, the two most common underlying health conditions were cardiovascular disease (32%) and diabetes (30%).2 Hospitalisations were six times higher among patients with a reported underlying condition (45.4%) than those without reported underlying conditions (7.6%). Deaths were 12 times higher among patients with reported underlying conditions (19.5%) compared to those without reported underlying conditions (1.6%).2 Two-thirds of people in the UK who have fallen seriously ill with COVID-19 were overweight or obese and 99% of deaths in Italy have been in patients with pre-existing conditions, such as hypertension, diabetes and heart disease.3 These conditions, collectively known as metabolic syndrome, are linked to impaired immune function,4 and more severe symptoms and complications from COVID-19.5

A major factor that drives the pathophysiology of metabolic syndrome is insulin resistance,6 defined as an impaired biological response to insulin, the hormone that regulates blood glucose levels. The dysregulation of blood glucose levels plays an important role in inflammation and respiratory disease. A study of patients with COVID-19 with pre-existing type 2 diabetes showed that those with better regulated blood glucose control fared better than those with poor blood glucose control.7 Specifically, well-controlled blood glucose (glycaemic variability within 3.9–10.0 mmol/L) was associated with reduced medical interventions, major organ injuries and all-cause mortality during hospitalisation, compared with individuals with poorly controlled blood glucose (glycaemic variability exceeding 10.0 mmol/L). Another study showed hospitalised patients with hyperglycaemia treated with insulin infusion had a lower risk of death from COVID-19 than patients without insulin infusion, likely due to reduced inflammatory mediators.8

The most significant factor that determines blood glucose levels is the consumption of dietary carbohydrate, that is, refined carbs, starches and simple sugars. However, the official dietary recommendations of most Western countries advocate for a reduced (low) fat, high-carbohydrate diet, which can exaccerbate hyperglycaemia. These dietary guidelines form the basis of menus in nursing homes and hospital wards where people with COVID-19 and pre-existing metabolic syndrome are undergoing recovery and respite.

The problem is not only confined to nursing homes and hospitals. As people self-isolate at home, many are stockpiling non-perishable staple foods that are cheap such as (carbohydrate-rich) pasta, bread, rice and cereal.9 Our food supply is dominated by highly processed, packaged foods; 71% of available food in the USA is classified as ‘ultra-processed’.10 Food and beverages such as pizza, doughnuts and fruit juices and other sugary drinks are likely to drive hyperinsulinaemia and inflammation, especially in those with metabolic syndrome.

Since the world is facing the rapid transmission of a novel virus, there has been little opportunity to conduct trials on whether patients with COVID-19 fare better on low-carbohydrate diets compared with other diets. However, there is robust evidence that restriction of dietary carbohydrate is a safe and effective way to achieve good glycaemic control and weight loss, and reduce the need for medication in the management of type 2 diabetes.11 12 A systematic review comparing low-carb diets to low-fat diets showed that the low-carb diets were superior for achieving glucose control, as well as for limiting cardiovascular risk factors in the short and long term for people with type 2 diabetes.13

There has been a reluctance to accept the benefits of low-carbohydrate diets, mainly because of the contradiction to official dietary guidelines which recommend that carbohydrates make up between 45 and 65 percent of total daily calories, but significant progress has been made in recent years. For example in 2018, Diabetes Australia released a position statement stating there was reliable evidence that lower carb eating can be safe and useful in reducing blood glucose levels, reducing body weight and managing heart disease risk factors such as raised cholesterol and raised blood pressure.14 Further, in 2019 the American Diabetes Association and in 2020 Diabetes Canada, both endorsed low carbohydrate diets as a viable option to improve glycaemia and the potential to reduce medications for individuals with type 2 diabetes.15 16

There are some medical institutions leading the way. One US-based hospital in West Virginia has answered calls to improve the food environment for its patients by removing all sugary drinks from its vending machines and cafeterias.17 The Jefferson Medical Center is also one of the first hospitals in the USA to offer low-carb meals to its patients with diabetes. Tameside Hospital in Manchester became the first in Britain to remove all added sugar from the meals it prepares for visitors and health service workers and it has taken sugary snacks and fizzy drinks off its menu.18

Restriction of dietary carbohydrates is a simple and safe intervention which results in rapid improvements in glycaemic control and can be implemented alongside usual care in a medical or domestic setting. While the pathophysiology of COVID-19 is multifactorial, insulin resistance is among the strongest determinants of impaired metabolic function. Since 88% of the US population is metabolically unhealthy,19 the extent to which it contributes to the severity of COVID-19 infection is likely to be significant. Therefore, the adoption of dietary advice for people with underlying metabolic syndrome as proposed in the UK,20 should be more widely endorsed by governments and policy makers globally, to mitigate the burden of pre-existing metabolic disease in those who contract COVID-19, now and into the future

Diabetes Canada Position Statement on Low-Carbohydrate Diets for Adults With Diabetes: A Rapid Review

1, Individuals with diabetes should be supported to choose healthy eating patterns that are consistent with the individual’s values, goals and preferences.

2. Healthy* low- or very-low-CHO diets can be considered as one healthy eating pattern for individuals living with type 1 and type 2 diabetes for weight loss, improved glycemic control and/ or to reduce the need for antihyperglycemic therapies. Individuals should consult with their health-care provider to define goals and reduce the likelihood of adverse effects. 3. Health-care providers can support people with diabetes who wish to follow a low-CHO diet by recommending enhanced blood glucose monitoring, adjusting medications that may cause hypoglycemia (sulfonylureas and insulin), or increase risk for DKA (SGLT2 inhibitors, underdosing insulin in those with insulin deficiency), and to ensure adequate intake of fibre and nutrients. 4. Individuals and their health-care providers should be educated about the risk of euglycemic DKA while using SGLT2 inhibitors and low-CHO diet, and further educated about the strategies to mitigate this risk (33).2 5. People with diabetes who begin a low-CHO diet should seek support from a dietitian who can help create a culturally appropriate, enjoyable and sustainable plan. A dietitian can propose ways to modify CHO intake that best aligns with an individual’s values, preferences, needs and treatment goals as people transition to or from a low-CHO eating pattern

Position Statement from Diabetes Australia

Low carbohydrate eating for people with diabetes

Key points

1. For people with type 2 diabetes, there is reliable evidence that lower carb eating can be safe and useful in lowering average blood glucose levels in the short term (up to 6 months). It can also help reduce body weight and help manage heart disease risk factors such as raised cholesterol and raised blood pressure.

2. For people with type 1 diabetes, a number of recent studies are reporting benefits of lower carb eating, however these studies are limited in their size and design and do not provide strong evidence of benefit. Diabetes Australia believes high quality, large scale, longerterm studies are necessary to further establish the effectiveness and safety of low carb eating for people with type 1 diabetes.

3. All people with any type of diabetes who wish to follow a low carb diet should do so in consultation with their diabetes healthcare team.

4. People with diabetes who commence low carb eating should monitor their blood glucose levels and, if necessary, talk to their doctor about the need to adjust their diabetes medication to reduce the risk of hypoglycaemia (low blood glucose).

5. People with diabetes considering low carb eating are encouraged to seek personalised advice from an Accredited Practising Dietitian experienced in diabetes management. There are some practical considerations that need to be taken into account to ensure the eating plan is safe and enjoyable, provides adequate nutrition for general health, is culturally appropriate and fits into the person’s lifestyle. 3

6. People with diabetes considering low carb eating should be aware of possible side effects (such as tiredness, headaches and nausea) and seek advice from their health care team if concerned.

7. Low carb eating may not be safe and is not recommended for children, pregnant or breastfeeding women, people at risk of malnutrition, people with kidney or liver failure, or those with a history of disordered eating or some rare metabolic conditions.

8. People with type 1 diabetes may experience sudden drops in blood glucose levels and be at a higher risk of hypoglycaemia when following a low carb eating plan. They should talk with their diabetes healthcare team before starting low carb eating.

All Australians should be encouraged to limit their intake of foods that are high in energy, carbohydrate or salt, including processed foods such as sugary drinks, chips, cakes, biscuits, pastries and lollies.

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