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Carbohydrate vs Fat: Is it really the great debate?

With current Australian and New Zealand nutrition guidelines recommending a wide range of total fat and carbohydrate intakes, emphasis is placed on quality and source rather than quantity of macronutrients, whilst limiting free sugars and saturated fat (1,2). These recommendations are similar around the world (3,4). However, in recent years these guidelines have been challenged, with some claiming carbohydrate rather than saturated fat should be restricted in the diet for optimum health. With opinions firmly divided, a great deal of confusion has arisen for health professionals and the public alike.

So what’s the story? New Zealand nutrition experts put the current debate into context, by providing clarity around the recommendations (5,6). Here’s what you need to know: 

We need to trust our current guidelines

Nutrition guidelines are not established lightly. As Mann and colleagues explain, “they are based on the totality of international evidence, from objective, systematic and thorough expert reviews of a range of studies, which evaluate the effects of foods and nutrients on health outcomes”(5).

Considering the growing obesity epidemic and associated co-morbidities, some claim the nutrition guidelines are not working. Both Australian and New Zealand recommend that 45-65% of total energy should come from dietary carbohydrates, preferably wholegrain, and 20-35% from fat, with no more than 10% total energy from saturated fat (1,2). Our most recent nutrition surveys show carbohydrate intakes sits at the lower end of the acceptable range and sugar consumption is declining, with both populations eating too little dietary fibre and too much saturated fat (2,7). With a small percentage of people meeting current guidelines in their entirety, it raises the question of whether it is an issue of compliance rather than the recommendations per se.

The ratio of carbohydrate to fat can vary within an optimal diet

While guidelines are consistent in recommending that intakes of free sugars and saturated fats be limited, they do allow a wide range of carbohydrate and fat intakes. These guidelines have been translated into a range of diverse dietary patterns around the world with evidence demonstrating they support good health. These include the traditional high-carbohydrate low-fat Japanese dietary pattern, associated with the greatest longevity worldwide, or the high-fat (in particular a high ratio of monounsaturated to saturated fats) Mediterranean diet, which is linked with lower rates of non-communicable diseases (6,8,9).

It is important to choose quality

A common thread shared between all healthy dietary patterns is a focus on quality choices. This is particularly true when it comes to the evidence behind carbohydrate and fat intakes.

There is a well-established evidence base that supports reducing intake of saturated fat is beneficial for heart health, provided the nature of the replacement energy source is taken into account (10,11). Replacing saturated fat with polyunsaturated fat reduces cardiovascular disease risk, however not when saturated fat is replaced with carbohydrates or protein (10). You can read more about this here.

A similar story is seen with substituting carbohydrates. While the need to reduce intake of free sugars has been widely acknowledged (12), the debate lies within the reduction of starches and non-starch polysaccharides. In comparison to fibre-rich grains, pulses, fruit and vegetables, foods containing rapidly digested starches are associated with higher blood triglycerides, lower HDL, and, in people with diabetes, higher blood glucose concentrations (6, 13). Whereas the consumption of slowly digested wholegrains and other fibre-rich starchy foods is associated with a reduced risk of some non-communicable diseases, including cardiovascular disease, diabetes, and colon cancer (6, 14).  Read more here.

Carbohydrate and fat are just two pieces of the puzzle

As Mann and colleagues explain, it’s time to stop pitting one nutrient against another. Debating over single nutrients opposed to foods and dietary patterns only feeds controversial headlines and fuels public confusion. This, in turn creates doubt around food choices, unhealthy relationships with food, and further incompliance of the evidence-based food and nutrition guidelines.

A need for consistent messaging from all health professionals and nutrition academics which draws on the commonalities shared in healthy eating patterns and lifestyles is paramount.  And, like the range of dietary patterns around the world that fit within current guidelines, the advice can too take on many forms if it is backed by evidence that underpins the recommendations. 

NEXT: Is the Health Star Rating working? 

References:

  1. National Health and Medical Research Council (2013). Australian Dietary Guidelines. Retrieved from https://www.nhmrc.gov.au/guidelines-publications/n55
  2. Ministry of Health (2015). Eating and Activity Guidelines for New Zealand Adults. Retrieved from http://www.health.govt.nz/publication/eating-and-activity-guidelines-new-zealand-adults
  3. Nordic Council of Ministers (2012). Nordic nutrition recommendations 2012. Part 1: summary, principles and use. Retrieved from http://www.norden.org/en/publications/publikationer/nord-2013
  4. US Department of Health and Human Services, US Department of Agriculture (2015). Scientific report of the 2015 Dietary Guidelines Advisory Committee. Part D. Washington, DC: US Department of Health and Human Services.
  5. Mann  J, Te Morenga L (2016). Nutrition experts defend dietary guidelines. Retrieved from http://www.otago.ac.nz/news/news/otago620115.html
  6. Mann, J et al (2016). Dietary guidelines on trial: the charges are not evidenced based. Lancet, 388(10047), 851-853. Retrieved from http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)31278-8/abstract
  7. Australian Bureau of Statistics (2014). Australian Health Survey: Nutrition First Results – Foods and Nutrients, 2011-12. Retrieved from http://www.abs.gov.au/ausstats/abs@.nsf/Lookup/4364.0.55.007main+features12011-12
  8. Mortality Trends. Trends in national mortality rates. Mortality Trends. Retrieved from http://www.mortality-trends.org
  9. Bloomfield HE, Koeller E, Greer N, MacDonald R, Kane R, Wilt TJ (2106). Effects on health outcomes of a Mediterranean Diet with no restriction on fat intake:a systematic review and meta-analysis. Ann Intern Med, 165(7): 491-500. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/27428849
  10. Hooper L, Martin N, Abdelhamid A, Davey Smith G (2015). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev, 6: CD011737. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/26068959
  11. Joint Food and Agriculture Organization of the United Nations, WHO Expert Consultation (2008). Fats and fatty acids in human nutrition. Geneva: Karger.
  12. WHO (2015). Sugars intake for adults and children. Geneva: World Health Organization. Retrieved from http://www.who.int/nutrition/publications/ guidelines/sugars_intake/en/
  13. Mann J, McLean, R, Skeaff M, Te Morenga L (2014). Low carbohydrate diets: doing against the grain. Lancet, 384: 1479–80.
  14. Ley SH, Hamdy O, Mohan V, Hu FB (2014). Prevention and management of type 2 diabetes: dietary components and nutritional strategies. Lancet, 383: 1999–2007.

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