Dietary patterns: what does it mean to eat healthily?

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Beth Meertens and Garry Jennings

Beth Meertens is an Accredited Practising Dietitian and Heart Foundation spokesperson on healthy eating and dietary patterns. Garry Jennings is the Heart Foundation's Chief Medical Officer.

Encouraging people to eat healthily isn’t easy. The topic of food and health is a quagmire of information for health professionals – let alone the public.

It’s hard to tell the difference between news headlines, study conclusions and what it means in the real world.

Recently, headlines accompanying several studies published in Lancet analysing Prospective Urban Rural Epidemiology (PURE) data are a case in point. Misleading news headlines read “Lower vegetable and fruit intake ok”, “Why carbs are more harmful than fat”, and “dietary guidelines need revisiting”.

So here’s our perspective on what these papers mean for the recommendations and practices of our health professional community.

Controversy grabs our attention, so it creates headlines. In such instances, details can be overlooked and meanings misconstrued.

Do these papers really turn dietary advice on its head?

The short answer is ‘no’. On closer reading of the papers – not the headlines –this research confirms existing recommendations for healthy eating from the Australian Government and Heart Foundation.

Overall, healthy eating patterns don’t rely on one type of food or one type of nutrient to promote health. They’re based on a combination of foods, chosen regularly, over time. Regular intake of the foods outlined in the Heart Foundation’s Heart Healthy Eating Principles will lead to sustainable dietary changes and promote heart health.

Check out our recent webinar and evidence review on dietary patterns for more information.

So why the controversy?

More than one factor is likely to be at play. Controversy grabs our attention, so it creates headlines. In such instances, details can be overlooked and meanings misconstrued.

For instance, finding an association (a relationship between two, or more, variables) is not proof of causation (the relationship between cause and effect). Such detailed, but crucial, information all too often gets lost in news headlines.

Also, media outlets often focus on individual studies, overlooking the fact that collective evidence carries far more weight than the findings of individual studies.

We’ve seen this previously with studies analysing the PURE data which reported higher cardiovascular risk with low intakes of salt. Then, news headlines called for relaxing of salt recommendations.

However, the studies had limitations. Salt was measured using spot urine measurements, which is an unreliable method. Also, reverse causality couldn’t be ruled out (those with lower salt intakes being sicker at the baseline). This meant this study didn’t overturn existing and consistent evidence on the benefit of lower salt intakes for cardiovascular health.

Focussing on ‘low’ or ‘high’ intakes doesn’t always give the full picture in nutrition studies. Quality, not just quantity, of the eating pattern is important. 

Existing advice and the PURE studies

Likewise, the recent PURE studies ( Miller et al , Dehghan et al , Mente et al ) don’t change existing advice – despite the controversy. In fact, they confirm what we already know.

Extreme diets

Extremes in dietary intake are associated with worse health outcomes. In one of these studies, very high carbohydrate intake (>70%), and very low-fat intake (<10%) were associated with a high risk of death from all causes, and death from non-cardiovascular disease, compared to more ‘moderate’ intakes (45-60%, and 20-35% respectively).

Neither the Heart Foundation, nor any other health body we know of, recommends dietary patterns that fall within these extreme ranges.

Quality matters

Fat and carbohydrate quality is what’s important.

Focussing on ‘low’ or ‘high’ intakes doesn’t always give the full picture in nutrition studies. Quality, not just quantity, of the eating pattern is important. In terms of quality, existing evidence demonstrates that roughly speaking, for heart health unsaturated is better than saturated fat is better than trans fat, while wholegrains are better than refined carbohydrates.

And such findings are confirmed in the PURE studies. The paper from Mente et al, for example, confirms existing evidence for cardiovascular risk that:

  • unsaturated fat is preferred over saturated fat, and
  • replacing saturated fat with carbohydrate provides no benefit.

This is consistent with other studies and the Heart Foundation’s position on dietary fat and carbohydrate quality.

The PURE authors suggest that carbohydrate targets around 55% and total fat targets around 35% are more appropriate than very high or very low intakes. This aligns with existing guidance from Australian NRVs and UK guidelines.

National and international dietary guidelines and Heart Foundation recommendations promote food sources of unsaturated fats and wholegrains/fibre. They also endorse limiting discretionary food and drinks which contribute excess saturated, trans fat, refined carbohydrates, added sugars and salt.

In practice, however, it’s more important to talk about food choices rather than focussing on precise amounts of nutrients.

Some possible areas of controversy exist with these studies’ findings. But, dig a little deeper and we find a little more to the story.

The devil is in the detail

As always, nuance matters. But headline writers may have interpreted study findings without considering their context and methodology.

Existing evidence demonstrates that wholegrains are protective for health outcomes, including the risk of dying from all causes, and cardiovascular disease. But this is seemingly at odds with some headlines arising from these PURE studies that “carbohydrate increases risk”.

In the study on total fat and carbohydrate intakes, total carbohydrate intake was not separated into good quality (i.e. wholegrains, fibre) and poor quality (i.e. refined carbohydrates, and sugar). However, the authors acknowledged that the high carbohydrate intakes observed in PURE (which were linked to a higher risk of mortality) were driven by high refined carbohydrate intakes.

The study on fruit, vegetables and legume intake found these foods were protective against risk of dying from all causes, and cardiovascular disease.

Fruit, vegetables and legumes contribute carbohydrates (and many other nutrients) to the diet, demonstrating that not all carbohydrates ‘are bad’.

Rather than ‘carbs are worse than fat’, a more appropriate headline would have been ‘an unbalanced diet with high intakes of refined carbohydrates increases health risks’. Not as catchy though…

Social factors are also a powerful force in health status.

As others have pointed out , it is likely that the extremes in dietary intakes (the really high carbohydrate and really low fat) seen in these studies were a marker of poverty. This may explain the relationship reported in the studies with these extremes and non- cardiovascular disease (CVD) mortality (i.e. dying from any cause except CVD) and the absence of a relationship with CVD mortality.

In all, the outcomes of this work do not change existing advice on dietary patterns and confirm some important things including the risk of extremes in dietary intake, and that quality of foods is important - not just quantity.

Controversy that wasn’t

Some possible areas of controversy exist with these studies’ findings. But, dig a little deeper and we find a little more to the story.

For example, the finding that predicting cardiovascular risk on one risk marker alone (i.e. LDL cholesterol) is not reliable in estimating the impact of diet on health outcomes. But this is consistent with Heart Foundation position on Absolute Risk , and that dietary counselling for dyslipidaemia should cover the entire eating pattern, not restricting just one nutrient.

Also, reducing saturated fat to <10% of energy was not supported by the PURE authors.
Remember, however, these studies include data from low and middle-income countries. This makes like-for-like comparisons problematic. It is hard to know how relevant the very low intakes of SFA seen in PURE (i.e. 3-5%) are to Australian dietary patterns (average intake ~13%).

Overall it is important to recognise that healthy eating does not rely on one type of food. Nor can we combat heart health risk factors by relying on one type of nutrient. Unfortunately, the narrow focus on one food or nutrient is usually where everyone gets tied up in knots.

PURE studies: strengths and weaknesses

Like many studies in the nutrition space, these studies were observational and so bring the usual strengths and limitations.

The strengths of these recently published studies include the large numbers in the cohort (around 135,000). What’s more, these populations from low, middle and high-income countries are not usually represented in dietary research.

These studies are an important contribution to the field of nutrition research, as they provide a bit more to the picture of healthy eating. But their limitations should be considered when interpreting results, including:

  • the diversity of populations
  • the near-impossible nature of controlling for socioeconomic status; and
  • that dietary intake was only measured at baseline (i.e. not regularly over time).

Take home message

In all, the outcomes of this work do not change existing advice on dietary patterns and confirm some important things including the risk of extremes in dietary intake, and that quality of foods is important not just quantity.

Our investigations into food and nutrition have demonstrated that habitual intake of the foods outlined in the Heart Foundation’s Heart Healthy Eating Principles will lead to sustainable dietary changes and promote heart health , based on evidence reviewed on the variety of dietary patterns associated with health outcomes.

This style of eating will be naturally lower in nutrients like refined carbohydrates, sugar, saturated fat, trans fat and sodium, and rich in nutrients like wholegrains, unsaturated fats and phytonutrients.

Adopting dietary patterns which align with these Principles could reduce the CVD risk by about a third globally.

Let the conflicting headlines play out. In the meantime, the best thing you can do is recognise that heart health does not hinge on one food or nutrient. Adopt the Heart Foundation’s Healthy Eating Principles to guide you and your clients through the nutrient-related noise.

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