What are the hardest things about switching to a low carb, higher fat diet for the sake of weight loss and better glucose control?
For the people who trialled the eating plan that forms the new CSIRO Low-Carb Diet, cutting their alcohol intake was one. But it wasn't just having less of something that was hard – eating more high fat foods like avocado and nuts was a big adjustment for some people, says senior research dietitian Pennie Taylor, co-author of The CSIRO Low-Carb Diet.
"Even though the message to eat a balance of healthy fats has been around since the early 2000s in Australia, some people are still wary of foods like nuts because they're high in fat," she says. "But rather than worry about how much fat we consume, we need to think about the quality of the fat we eat."
It's the definition of healthy fat that makes the CSIRO's low carb higher fat approach different to low carb diets that embrace saturated fats like lard, butter, duck fat and coconut oil. Instead, the CSIRO takes a cautious approach to saturated fat and suggests keeping intake low.
"We acknowledge that there's a debate about the health effects of saturated fat. Although past evidence suggests saturated fats have a role in heart disease, more recent evidence suggests the relationship may not be so strong – but there are still questions that need to be answered," Taylor says.
But dairy fat may be an exception.
"Although it's a saturated fat, research has found that full fat dairy foods don't increase the risk of heart disease – it may be that the package of nutrients in dairy foods as a whole is protective. Although we recommend low fat dairy products in the diet, that's because reduced fat versions are higher in calcium than full fat dairy and we were conscious of reducing kilojoules," she adds.
So, for now, the good fats this diet promotes are mono unsaturated fats (in avocado, almonds, cashews hazelnuts and peanuts and olive oil) and polyunsaturated fats (in oily fish, walnuts, pine nuts, pecans, Brazil nuts, sunflower and flax seeds). What makes them so good, says Taylor, is that they slow down the rate at which digested food leaves our stomach – and therefore help keep blood glucose levels steady and help control appetite improve levels of blood fats like cholesterol and triglycerides make us feel full and prevent overeating – and increase the pleasure of the meal.
The rationale behind this low carb diet that combines just 50 to 70g carbohydrates daily (the equivalent of three to four and a half slices of bread) with higher intakes of protein and fat is the CSIRO's 2012 to 2014 study comparing the effects of two diets on a group of overweight or obese people with diabetes. One group ate the low carb diet high in healthy fats; the other ate a healthy high carb, low fat diet. After 12 months of combining these diets with an exercise plan, both groups lost 10 kilograms. But there were extra benefits for the low carb group: healthier levels of blood fats, better blood glucose control and a significant reduction in diabetes medication.
Still, Ms Taylor is the first to say that there's no one best diet for everyone and this low carb approach is designed for particular people such as those who are overweight (that's more than 60 per cent of us), those with type 2 diabetes (around two million of us), people with insulin resistance – and should be combined with support from a dietitian and regular health checks.
But before we all slash our carb intake, the debate about how much carbohydrate is best raises some issues says dietitian Matt O'Neill who recently convened a webinar Low Carb Diets - Fad or Future? with Ms Taylor and nutrition scientist Dr Tim Crowe.
One issue is that the long term effects of following low carb, higher protein diets beyond about two years are unknown. Another is that if we could stick with healthier lifestyle habits throughout life we might not need to cut carbs so dramatically.
"There's a case for a low carb approach but it's also a bit like a sledgehammer – yet if we're prepared to set as a priority doing more exercise, making sure we get more sleep, reducing stress and taking a mindful approach to eating then maybe we can afford to eat more good quality carbohydrates and still manage blood sugars," he says.
"Perhaps we also need to look at two sets of dietary guidelines for the future – a lower carb version for people who are overweight and at risk of type 2 diabetes and a regular carb version for those who are lean and more physically active and who use other lifestyle measures to maintain a healthy weight."
The CSIRO Low-Carb Diet by Associate Professor Grant Brinkworth and Pennie Taylor is published by Macmillan Rrp $34.95