Why have dietary guidelines become such a focal point of nonsensical arguments?
Like much contemporary noise in nutrition, the hard-chargers come from the low-carb world, particularly its “ancestral” first cousin. In 2016, a report published by a low-carb pseudoscience advocacy group known as the “Public Health Collaboration” stated that the UK dietary guidelines were “corrupt”, and had: “driven people away from highly nourishing, wholesome, and health-promoting foods.”
As you might guess, butter and meat were those “nourishing, wholesome” foods. The report stated:
“The flawed science behind this message and subsequent change in dietary guidelines introduced for Americans in 1977 followed by the UK…in 1983 has resulted in increased consumption of low fat junk food, refined carbohydrates and polyunsaturated vegetable oils. The conspicuous rise in obesity immediately following their introduction suggests that they are a root cause of the problem.”
No doubt you are all overly, and tragically, familiar with this line of reasoning at this point. This common claim holds that dietary guidelines were a cause of increased levels of non-communicable diseases in the population over the period following their introduction.
But this is an empirical claim. Which means we can test this claim by reference to empirical evidence.
Adherence to Dietary Guidelines and Long-term Health Outcomes
A good example of the relationship between adherence to dietary guidelines and long-term health outcomes was provided in a 2021 analysis by Ewers et al. of the Copenhagen General Population Study. Diet was assessed based on the Danish dietary guidelines, which are similar to most other national dietary guidelines in Western countries, and included the following key recommendations:
- Eat less saturated fat
- Eat plenty of vegetables and fruit
- Eat more fish
- Eat less sugar
- Eat lower salt foods
The exposure of interest was adherence to the dietary guidelines, categorised into levels of adherence according to how many of the five recommendations an individual met. For the analysis, the highest level of adherence to the dietary guidelines was the reference category against which other levels of adherence were compared.
100,191 participants provided complete dietary data for the analysis, which covered up to 14 years of follow-up [average of 9.2 years], in which 9,273 deaths occurred.
Compared to the highest level of adherence, the lowest level of adherence was associated with 35% [HR 1.35, 95% CI 1.11—1.64] higher risk of death from cardiovascular disease [CVD]. Similarly, for all-cause mortality, the lowest adherence level was associated with 46% [HR 1.46, 95% CI 1.32—1.62] higher risk of death from all causes.
This is hardly persuasive for deliberately advising people not to adhere to dietary guidelines, is it?
Now, you could point out that the Ewers et al. analysis might tell us about low adherence, but not necessarily whether high adherence lowers risk, and how strong any such association may be. Several analyses have, however, used the lowest level of adherence as the reference category against which to compare the risk associated with high levels of dietary guidelines adherence.
Kebbe et al. investigated the associations between universal dietary guidelines based on the four main World Health Organisation [WHO] dietary recommendations and mortality risk in the UK Biobank cohort. The exposure of interest was adherence to the following recommendations:
- Saturated fat <10% energy
- Added sugars <10% energy
- Dietary fibre >25g per day
- Fruit and vegetables >5 servings [~400g] per day
The primary analysis categorised participants based on the number of recommendations met: 0, 1, 2, or 3-4. A secondary analysis was also conducted based on each individual recommendation.
Compared to the reference group of 0 recommendations, those meeting 2 recommendations had a 9% [HR 0.91, 95% CI 0.85—0.97] lower risk of all-cause mortality. However, those meeting 3–4 recommendations had a 21% [HR 0.79, 95% CI 0.71—0.88] lower risk of death from any cause. Compared to the reference group of 0 recommendations, those meeting 3–4 had a 22% [HR 0.78, 95% CI 0.61—0.98] lower risk of death from CVD.
Similarly, Scheelbeek et al. conducted a meta-analysis of the associations between meeting 0–2, 3–4, or 5–9 of the UK’s national dietary guidelines in three UK cohorts. They found that the highest adherence category was associated with 7% [RR 0.93, 95% CI 0.90–0.97] lower risk of all-cause mortality.
Thus, lower adherence to dietary guidelines is associated with a higher risk of adverse health outcomes, while higher adherence is associated with a lower risk.
This is a replicable, reproducible finding in different populations.
Does Anyone Follow the Guidelines?
We can add weight to the refutation of common claims made against dietary guidelines by considering just how prevalent adherence to the guidelines is.
Consider that in the UK Biobank cohort analysed by Kebbe et al., only 9.5% of the overall cohort [9,712 of 115,051 participants] met 3–4 of the recommendations. In the analysis by Scheelbeek et al. using National Diet and Nutrition Survey data in the UK, less than 0.1% adhered to all nine national UK dietary guideline recommendations.
A 1984 study of British dietitians following the introduction of the UK dietary guidelines found that only 10% met the recommendation for fat intake, and 7% met the target for fibre intake. An analysis of time-course trends in the UK population by Yau et al. showed that at three years after the introduction, just 8.3% met the targets for fruits and vegetables.
The guidelines were never really followed. By anyone.
Thus, if the contention is that following the guidelines is associated with worse health outcomes, then this is also demonstrably falsifiable. It is an empirical claim unsupported by any empirical evidence.
Cumulatively, there is little to no evidential wiggle room to argue that dietary guidelines are either:
- Followed by any substantial proportion of the general population
- Associated with increased risk if they are adhered to
- Associated with better health if they are not adhered to.
The search for convenient scapegoats should really move on from the dietary guidelines.
A Congruent Evidence Base
Ah, you hear the sophists say, but this is observational research! You hear mutterings of “association isn’t causation” and other lowly critiques. So let’s start with this, because unbeknownst to the talking heads, there is evidence from RCTs that corroborate the efficacy of dietary guidelines in reducing disease risk.
In the CRESSIDA study, the intervention group were counselled according to the UK dietary guidelines, emphasising low saturated fats, polyunsaturated-enriched margarine, olive oil, wholegrains, and oily fish. This group were compared to a control group consuming a “typical British diet pattern” with butter spreads, refined grains and cereals.
At baseline, all subjects had dietary characteristics that reflected population averages for total fat, saturated fat, and salt. Over 12 weeks, the dietary guideline intervention group reduced body weight, blood pressure and blood cholesterol levels. These changes reflected an increase in fibre, a reduction in added sugars and sodium, an increase in omega-3s, and a reduction in saturated fat.
The reductions in blood pressure and cholesterol observed with adherence to the dietary guidelines would be predicted to reduce the risk of fatal CVD by 15% and nonfatal CVD by 30%.
The Dietary Guidelines are Good for You
At this point, we should be able to put questions over dietary guidelines, whether at the national level or universal WHO recommendations, to bed.
The papers that are most cited in support of the contention that dietary guidelines are not evidence-based, all derived from the same lunatic author [Zoe Harcombe] in the same journals [BMJ Open Heart and British Journal of Sports Medicine]. These journals respectively bear about as much resemblance to the truth of nutrition science as the Republicans to U.S. election results.
Yet how many nutrition professionals and coaches, if asked what they recommend to clients, would say, “I recommend that they aim to follow the dietary guidelines”? There is a lesson in all of this that I think is important for nutrition practitioners to hold dear; that the best practices are the ones right in front of us.
You are not a lesser nutritionist because you help someone achieve dietary guideline recommendations over the latest macro-split-intuitive-eating-intermittent-fasting bastardisation festering around the Internet. You’re actually better for it.
Yours in Science,
Alan
Learn with Us.
You’ll find our most comprehensive resources in the Alinea Nutrition Education Hub.
Our weekly Deepdive takes a take a forensic look at a recent study: you’ll understand the background, the findings, and the relevance of the study in the context of the wider literature.
Our bi-monthly video Research Lectures condense complex topics into a visual presentation for you to maximise your learning experience.
And Exclusive Articles from researchers and academics in the field of nutrition science provide insights and perspectives from the people producing the research.