An Australian study has shown carbohydrate intake may have a greater impact on cardiovascular disease (CVD) risk in women than saturated fats.

The observational study assessed the effect of carbohydrate and saturated fat intake on CVD risk in 9,899 middle-aged Australian women, logging 1,199 CVD incidents and 470 deaths over 15 years.

It found higher carbohydrate intake (41%–44% energy as carbohydrate) conferred a lower CVD risk compared to the lowest carb intake, less than 37%, (OR: 0.56). Carbohydrate intake didn’t affect mortality, however.

Contrary to conventional wisdom, study co-author Associate Professor Sarah Zaman and her team found no association between saturated fat intake and CVD or mortality.

Further, increasing saturated fat and carbohydrate intake significantly reduced hypertension, diabetes and obesity risk, according to Associate Professor Zaman, an Academic Interventional Cardiologist at Westmead Hospital and University of Sydney.

While the cause of inconsistent saturated fat and CVD findings are unclear, “it has been suggested that historical studies neglected to adjust for fibre, which is known to be anti-atherogenic,” the authors wrote.

“In addition, it has been shown that saturated fat increases large low-density lipoprotein (LDL) particles rather than the small, dense LDL particles that are strongly related to CVD.”

“This may explain why saturated fat intake could increase overall LDL-cholesterol levels without impacting CVD risk.”

Sex differences in diet and CVD risk

Though the findings are “interesting”, Associate Professor Sarah Zaman felt cardiologists and dietary guidelines shouldn’t change their health advice just yet.

“We definitely should wait for further research [before changing advice on carbohydrate and saturated fat intake]”, she told the limbic, noting that while her work was a good prospective study, large randomised clinical trials are needed to establish causation.

In particular, these trials should look at sex differences in diet-associated CVD risk, she said.

So far there hasn’t been a lot of research into sex differences in diet, but “we know that women have different risk factors for heart disease, the onset of heart disease can be a bit later in women versus men and that heart disease can present differently in women,” she said.

Current dietary guidelines largely rely on trials with predominantly male participants or without sex-specific analyses, her paper read.

“But, given we’re seeing these emerging sex differences in so many other factors, I do think we need to look at it in diet,” Associate Professor Zaman said.

Future research should also look at the types of macronutrients that modulate CVD risk.

“At the moment we’ve really just looked at macronutrient intake . . . so even though we can say moderate carbohydrate intake had the best result in terms of reducing heart disease, I think there’s going to be big differences if you look at processed carbohydrates versus non-processed carbohydrates and similar for your fats,” she said.

In the meantime, Associate Professor Zaman said greater cardiologist-dietician collaboration could help support food-related CVD prevention.

“I think it would be an excellent step to have more of a multidisciplinary approach to our patients.”

“We do for secondary prevention, so when someone’s come into the hospital, say for a heart attack, they get referred to cardiac rehabilitation and that, of course, includes a dietary component and it is delivered in a multidisciplinary way.”

“But, if you’re talking primary prevention, it’s a bit more disjointed — patients probably get referred by their GP, they may or may not see a dietician, they might see a cardiologist who might give them advice, but it might be different to what the dietician’s advice is — so it’d be great if we had a bit more of a collaboration.”