In the 1970s, low-carb diets were all the rage. The Dr. Atkin’s Diet Revolution book claimed carbohydrate restriction was a “high calorie way to stay thin forever.”
Carbohydrates are found in breads, cereals and other grains, fruit, vegetables and milk. They’re also in ultra-processed fast foods, cakes, chips, and soft drinks.
These days, low-carb diets are promoted as a weight-loss solution, to beat heart disease and as better for diabetes. But how do these claims match up with the latest research?
A new review of the evidence found long-term low-carb dieters lost just under a kilo more weight than other dieters. However the review concluded there was no evidence low-carb diets have any additional health benefits.
In fact, if you’re on a low-carb diet, you’ll need to pay closer attention to what you eat to make sure you get enough essential vitamins, minerals, dietary fiber and other phytonutrients.
The Cochrane review included 61 randomized controlled trials (the highest level of evidence) with almost 7,000 adults with excess body weight. About 1,800 had type 2 diabetes. People in the healthy weight range were not included.
The reviewers compared weight-loss diets that varied in carbohydrate content:
• lower carbohydrate diets. This included very low-carb or ketogenic diets (less than 50 g of carbs a day or less than 10% of your total energy from carbs) and low-carb diets (50-150 g of carbs per a day, or less than 45% of total energy from carbs)
• “balanced” carbohydrate diets (150+ grams of carbs a day, or 45-65% of your total energy from carbs)
The reviewers found that among adults with excess body weight (but who didn’t have type 2 diabetes), those following lower-carb diets for three to 8.5 months lost, on average, one kilogram more weight than those on balanced carb diets.
However, when they ensured restrictions in energy intake were the same in both groups, by providing the food or meal plans, the difference was about half a kilogram.
In longer-term weight-loss interventions lasting one to two years, the average difference in weight-loss between those on low-carb versus balanced carb diets was just under one kilogram.
The average weight lost by groups on any weight-reducing diet varied greatly across the trials from less than one kilogram in some, up to about 13 kg in others.
The studies in adults with type 2 diabetes found greater initial weight loss on low-carb diets compared to balanced carb diets: 1.3 kg over three to six months. However, in longer interventions that lasted between one to two years, there was no difference.
In the small group of studies that included a maintenance period at the end of the weight-loss intervention, there were no differences in weight-loss in adults either with or without type 2 diabetes.
There were no significant differences in other health measures, including blood pressure, cholesterol, blood sugar control, or risk of constipation. And they found no important clinical differences in results based on the extent of participants’ carb restriction.
Overall, the review shows that whether you prefer a lower carb or a balanced carb eating pattern, both can work for weight loss.
Carbohydrate is a macronutrient. Your body uses it to produce energy to fuel your muscles, brain, lungs, and other vital processes.
Healthy foods with carbs —breads, cereals and other grains, fruit, vegetables and milk — are packed with other important nutrients, especially dietary fiber, thiamine, calcium and folate.
Without careful planning, a low-carb diet could also be lower in these nutrients. So how can you ensure you’re consuming enough? Here’s what to look out for — and some lower- and higher-carb options.
Dietary fiber is needed to keep your bowel function regular and promote growth of healthy bacteria in your colon.
Lower carb sources: spinach, fresh and frozen mixed berries, almonds, cauliflower
Higher carb sources: wholegrain bread, apples, chick peas, sweet potato.
Thiamin or vitamin B1 is needed to supply energy to your body’s tissues and is used to metabolize carbohydrates.
Lower carb sources: trout, tuna, sunflower seeds, beef, yeast extracts
Higher carb sources: brown rice, black beans, whole meal bread, yoghurt.
Calcium is needed for strong bones.
Lower cab sources: hard cheese, canned salmon with small bones, almonds, firm tofu
Higher carb sources: yoghurt, milk, soft cheese.
Folate is essential for growth and is used to manufacture DNA, your genetic code. Adequate intakes are especially important for women, as folate is needed to prevent neural tube defects in infants during pregnancy.
Lower carb sources: green leafy vegetables, avocado, broccoli, peanuts
Higher carb sources: whole meal bread (Australian bread-making flour is fortified with folic acid), fortified wholegrain cereals, brown rice, oranges.
Ultimately, if you love carbs and want to lose weight, you can. Plan to lower your kilojoule and carb intake by not eating ultra-processed, energy-dense, nutrient-poor (junk) foods, while still eating carbohydrates from healthy foods.
Clare Collins is a Laureate Professor in Nutrition and Dietetics at the University of Newcastle, NSW and a Hunter Medical Research Institute (HMRI) affiliated researcher. She is a National Health and Medical Research Council (NHMRC) Leadership Fellow and has received research grants from NHMRC, ARC, MRFF, HMRI, Diabetes Australia, the Heart Foundation, the Bill and Melinda Gates Foundation, the nib foundation, Rijk Zwaan Australia, WA Deptartment Health, Meat and Livestock Australia, and Greater Charitable Foundation. She has consulted to SHINE Australia, Novo Nordisk, Quality Bakers, the Sax Institute, Dietitians Australia and the ABC. She was a team member conducting systematic reviews to inform the 2013 Australian Dietary Guidelines update and the Heart Foundation evidence reviews on meat and dietary patterns.
Erin Clarke and Rebecca Williams are affiliated with the School of Health Sciences, College of Health, Medicine and Wellbeing, The University of Newcastle, NSW, Australia.