By Claire McDonnell Liu, Nutritionist at Leafie.org
Heart disease is the leading killer of people worldwide, responsible for an astronomical 17.9 million deaths each year.
A healthy diet is key to preventing cardiovascular disease (CVD) risk, and its risk factors such as diabetes and obesity.
In a recent scientific statement, ‘Popular Dietary Patterns: Alignment With American Heart Association 2021 Dietary Guidance’, published by the American Heart Association (AHA) popular diets were assessed and ranked for heart health.
The heart association placed Ketogenic and Very Low Carb (VLC) diets lowest for heart health, which prompted cautionary headlines around the globe. But is this the complete picture?
Heart Association Analysis of Diets
Ranking highest for optimal heart health in the AHA diet assessment were four predominantly plant-based diet patterns: Mediterranean; DASH [Dietary Approaches to Stop Hypertension]; pescetarian; and vegetarian. “The conclusion that we came away with between these diets is that they’re all fine and very consistent with a heart-healthy diet,” said Christopher D. Gardner, the director of nutrition studies at the Stanford Prevention Research Center and chair of the committee that wrote the report.
The inclusion of red meats and foods rich in saturated fat whilst limiting carbohydrates that align with the AHA’s dietary principles, such as beans, whole grains, starchy veggies, and fruits, were seen as negatives for ketogenic and low-carb diets in the analysis.
The AHA ranking process also took into account factors such as whether the diets allowed flexibility for cultural needs, preferences and budgets, areas where keto and low carb patterns were deemed to score lower than diet patterns that limit meats and dairy.
The AHA analysis was not a systematic review of diet interventions for heart health. Instead, diet patterns were evaluated to see how closely they aligned with AHA guidelines for heart-healthy eating. The diets that scored highest were those that align with the AHA’s dietary own dietary tenets. Eminent nutrition researcher and author Nina Teicholz notes this key point in her recent Unsettled Science substack article ‘Is Keto Bad for the Heart?‘, stating that “By this standard, the #1 diet on their list is DASH, because…that’s the AHA’s own diet! The AHA report was a self-affirmation exercise, a purity test. Headlines should have read: the AHA likes its own diet best and disapproves of others”.
Low Carb Benefits for Heart Health
A randomised trial published in May, since the AHA diet ranking, compares VLC with the DASH diet. The Comparing Very Low-Carbohydrate vs DASH Diets trial found that for adults with hypertension, prediabetes or type 2 diabetes, and overweight or obesity, “the VLC diet resulted in greater improvements in systolic blood pressure, glycemic control, and weight over a 4-month period compared with the DASH diet”. This trial demonstrates that a VLC diet outperforms the AHA’s preferred diet for improving heart health risk factors, including reducing blood pressure, also called hypertension, which the DASH diet is designed to treat.
Significantly the AHA diet ranking statement also highlights the cardiovascular and metabolic health “improvements in weight and measures of glycemia with these patterns” found in a number of studies related to VLC and Ketogenic diets. Whilst acknowledging that very low-carbohydrate / ketogenic diets have been shown to “improve CV risk factors, including blood glucose, body weight, triglycerides, and high-density lipoprotein cholesterol, in studies up to 6 months”. In addition, Ketogenic and Low carb Diets are known to help with weight loss, a significant risk factor for heart disease.
The AHA report also highlights further keto and low-carb diets benefits: “a Keto or low carb diet has particular strengths, including an emphasis on non-starchy vegetables, nuts, and fish, minimal intake of foods and beverages with added sugar, and limited alcohol consumption”.
Evidence not assumptions
Heart disease presents a significant public health catastrophe, and advice from public bodies on healthy eating to reduce risk should be taken seriously. That said there are a few salient questions worthy of more consideration lurking behind the ominous headlines.
LDL Cholesterol as a stand-alone health marker?
Criticism of ketogenic diets for heart health typically stems from concerns that eating more fat or lower carbohydrates may increase risk of heart disease or death due to elevated LDL cholesterol levels.
A key consideration is whether LDL cholesterol as a stand-alone heart health marker demonstrates cardiovascular risk absolutely, rather than being considered as one factor of a number of heart and metabolic health markers. For instance, a 2018 clinical research study found improvements for a number of CVD risk biomarkers for diabetes patients in nutritional ketosis after 1 year, whilst LDL-cholesterol particle size increased.
Dr Paul Mason sets out the significant pitfalls of relying on LDL cholesterol alone in a recent presentation for Low Carb Down Under: ‘The Truth About Cholesterol’.
Is the evidence satisfactory?
Public health dietary advice to reduce catastrophic levels of population disease advice should be based on the best practice evidence possible. A factor to consider then is how nutritional data is acquired in cardiovascular dietary studies, and could higher quality evidence be prioritised.
Assumptions relating to keto or low-carb diets for heart health may be based on data derived from observational or epidemiological studies, which involve inherent bias, rather than from best practice evidence from Randomised Control Trials (RCTs).
Data from epidemiological studies may be skewed by a number of factors, such as:
- Relying on participants to recall foods in retrospective food questionnaires.
- Multiple confounding factors: for instance, someone eating a particular dietary pattern may also increase exercise, avoid stressors, smoking or alcohol.
- Diet quality or levels of food processing that may impact on disease risk factors may be overlooked.
Currently, data from clinical intervention trials that specifically measure cardiovascular risk for people on ketogenic or very low-carb diet therapy is in short supply. We cannot, therefore, demonstrate that study participants following a keto or low-carb diet have more cardiovascular disease, heart attacks or strokes. The inverse is also true, in that we have had limited evidence to date that demonstrates that a ketogenic diet reduces cardiac events, until the recently published 4-month randomised trial Comparing Very Low-Carbohydrate vs DASH Diets demonstrated reduction in CVD risk markers. This randomised trial marks a significant landmark in dietary research for heart health, as a 4-month ‘gold standard’ trial focused on dietary interventions for heart health.
Is it even Low-Carb?
Low-carbohydrate diet studies have been found to be, well, not low-carb…
Some ‘Low Carb or Keto diet research studies have been shown to be based on carbohydrate levels that, although lower than the Standard American Diet, would not be considered within the very low-carbohydrate or ketogenic macronutrient range.
For example, a study presented at the American College of Cardiology’s Annual Scientific Session Together With the World Congress of Cardiology suggested that a “keto-like” diet may be associated with higher blood levels of “bad” cholesterol and a doubled risk of cardiovascular events such as chest pain (angina), blocked arteries requiring stenting, heart attacks, and strokes. This study defined a Low-Carb or Keto diet as consisting of no more than 25% of total daily energy or calories from carbohydrates and more than 45% of total daily calories from fat. They dubbed this a “keto-like” because it is “somewhat higher in carbohydrates and lower in fat than a strict ketogenic diet”. However, at 25% total energy from calories of a 2000-day calorie diet would represent around 130g carbohydrates per day, more carbohydrates than most people on a keto diet would eat in a week – and most importantly would not likely be able to establish nutritional ketosis.
Other studies set a carbohydrate limit at 40% of energy from carbohydrates, approximately 200g of carbohydrates per day, which again would be well above VLC or ketosis diet ranges.
This is a significant point, as attention-grabbing headlines warning about the dangers of low-carb nutrition may not be assessing a VLC or Keto diet at all.
- Very low-carbohydrate (less than 10% carbohydrates) or 20 to 50 gm/day
- Low-carbohydrate (less than 26% carbohydrates) or less than 130 gm/day
- Moderate-carbohydrate (26% to 44%)
- High-carbohydrate (45% or greater)
Should we adjust for carbohydrate intolerance in unhealthy populations?
Large numbers of our populations are affected by diet-related chronic diseases. Diabetes type 2 and metabolic conditions may be better controlled or reversed with carbohydrate restriction, making Keto or low-carb diets highly relevant options to the high numbers of people affected.
Those with an intolerance to carbohydrates may be at risk from blanket recommendations to opt for “heart-healthy” carbohydrate-high diets, based primarily on grains.
We also know that many factors combine to form the best dietary pattern for an individual, so a one-size-fits-all approach would not appear to be the best-practice approach to public dietary advice, particularly given the exponential rates of non-communicable disease.
Should Seed Oils be promoted as heart-healthy?
Diet patterns that include plant-based oils scored highest in the AHA analysis, whilst diets “lost points for restricting nuts and healthy (non-tropical) plant oils“.
This promotion of plant-based seed oils, also known as vegetable oils, from the AHA may cause some confusion within populations due to mounting concerns over potential harm from industrially produced seed oils.
Some analysis suggests that dietary linoleic acid, especially when consumed from refined omega-6-rich vegetable oils may increase cardiovascular risk. DiNicolantonio and H O’Keefe set out evidence to this point in 2018 article “omega-6 linoleic acid promotes heart disease“. “Numerous lines of evidence show that the omega-6 polyunsaturated fat linoleic acid promotes oxidative stress, oxidised LDL, chronic low-grade inflammation and atherosclerosis, and is likely a major dietary culprit for causing CHD, especially when consumed in the form of industrial seed oils commonly referred to as ‘vegetable oils’”.
Not The Last Word for Heart Health Diets
The current wave of headlines around keto diets being last for heart health may be considered misleading.
The AHA analysis highlights some significant CV benefits for heart health with a very low carb (VLC) or ketogenic diet pattern, and further recent RCT found the VLC to be superior to DASH diets for heart health markers for those with type 2 diabetes.
Further research is vitally important and should be welcomed into keto and low-carb diets and heart health. Meanwhile, personal health checks focusing on a range of cardiovascular and metabolic health markers appear to be key in managing personal risk, whilst the science evolves.