14 Nov 2022 — The European Food Information Council (EUFIC) has questioned a recent study on the impacts of a low-carb diet, stating that it misrepresents the health effects on patients with diabetes and may harm sufferers. The study researchers at Tulane, however, do not necessarily disagree with the EUFIC’s statements.
The study found that a restricted calorie, low-carb diet reduced blood sugar levels 0.22% more participants than following their usual diets over a six month period, but the EUFIC says the reasons for these results are unclear.
NutritionInsight speaks to diabetes epidemiology researcher at Tulane University in New Orleans, Louisiana, US, and the study’s lead author, Dr. Kristen Dorans and Laura Bosman, content creator for the EUFIC, about what these findings mean and how they can be applied to future diabetes research.
“Dietary restriction may be associated with adverse health effects in the longer term, and many carbohydrate-containing foods, such as fruit, vegetables and whole grains contain components important for health like vitamins, minerals and dietary fiber,” says Bosman. “Following a strict low-carb diet, therefore, may lead to nutrient deficiencies.”
“The study’s key message is that a low-carbohydrate diet, if maintained, might be a useful approach for preventing and treating Type 2 diabetes, though more research is needed,” Dorans retorts. “We already know that a low-carbohydrate diet is one dietary approach used among people who have Type 2 diabetes, but there is not as much evidence on effects of this diet on blood sugar in people with prediabetes.”
Study design and limitations
It may be impossible to differentiate the effects of low-carb, calorie restrictive diets and the weight loss they induce.
The randomized clinical trial, published in Jama Network Open, divided 150 adults (108 women and 42 men) aged 40 to 70 into two parallel groups and traced the results of a low-carb diet over six months. They were further split into two groups where they either maintained a low-carb diet or adhered to their usual diets.
Additionally, the study excluded those taking glucose-measuring medications and those with Type 1 diabetes to more accurately test the diet’s effects on blood sugar levels. Specifically, the researchers measured HbA1c – a type of hemoglobin that reveals how well your body has absorbed sugars over a two to three-month period.
Participants were prescribed diets of less than 40 g of carbohydrates a day for the first three months with the option of increasing intake to less than 60 g for the second three months. The results found that the low-carb group decreased their HbA1c by 0.26%, while those following their usual diets decreased their HbA1c by 0.04%.
“While the study was overall well-designed, some limitations remain,” states Bosman. As highlighted in our article, the researchers were unable to assess the effect of a low-carb diet on HbA1c levels independently of weight loss – this is a limitation because excess body weight is considered one of the main risk factors for Type 2 diabetes. ”
“Therefore, it remains unknown whether the positive effect of a low-carb diet was due to weight loss itself or any other factor associated with the diet,” she adds.
“In regards to dietary approaches for people with prediabetes, the American Diabetes Association published a consensus report in 2019,” Dorans underscores.
She quotes the report directly, saying “it concluded that ‘Evidence suggests that there is not an ideal percentage of calories from carbohydrate, protein, and fat for all people with or at risk for diabetes – therefore, macronutrient distribution should be based on individualized assessment of current eating patterns, preferences, and metabolic goals.’”
A further limitation the EUFIC highlights with the study was that it was too short and included too small and too specific of a population that may not be representative of other groups.
“The effectiveness of a low-carb diet has to be further studied and over longer time periods in other populations and settings before it can be adopted as a dietary tool for type 2 diabetes prevention,” Bosman affirms.
Moreover, Bosman holds that, since the test group was given instruction and advice on meal planning, another limitation of the study is the “intensive dietary counseling” given to the low-carb group, which may not be readily available to those with Type 2 diabetes or prediabetes.
“There is some evidence to show that, with careful planning, a low-carb high-fat diet can help manage Type 2 diabetes and can result in greater weight loss for individuals with obesity compared to low-fat diets,” Bosman acknowledges.
“Any weight loss that occurs is most likely a result of a calorie deficit created from cutting out the energy-dense foods, and sticking to extremely low-carb diets may not be a practical and sustainable long-term option for many people,” she maintains.
Not necessarily a point of contention
Doran does not disagree with Bosman’s assertions. “Most of the key points made in these critiques are similar to the limitations that we noted in the ‘Discussion’ section in our paper, so I don’t have much to add,” she says.
“I agree that future research should study glycemic effects of low-carbohydrate diets over longer periods of time and in other populations.”
Furthermore, Doran also highlights the dangers of attempting a low-carb diet without counseling. “Importantly, anyone taking diabetes or blood sugar-lowering medications should talk with their doctor before changing their diet,” she asserts.
Though the EUFIC and the Tulane researchers appear to agree on these points, Bosman identifies other problems with carbohydrate restriction.
“Eliminating food groups unnecessarily from the diet can create a negative relationship with food, which in extreme cases can lead to eating disorders,” she notes. “It’s important to remember that balance, variety and portion control are key.”
In related news, New York City’s public hospitals have made plant-based meals the main option for patients to help lower the risk of diabetes and cardiovascular diseases, citing recommendations by organizations such as the American Diabetes Association, the American Heart Association and the American Medical Association.
By William Bradford Nichols
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