Plant-based eating patterns have a number of characteristics which may contribute to their role in heart health. Plant-based foods such as fruit, vegetables, legumes, whole grains, nuts and seeds are lower in saturated fat and many are a source of fibre. A diet low in saturated and providing unsaturated fat is important for maintaining a healthy cholesterol level. In addition, specific plant foods or components have been shown to reduce blood cholesterol, e.g. soya protein, nuts, oat/barley beta glucans and plant stanols or sterols.
Lower intake of saturated fat coupled with higher intake of polyunsaturated fat helps to lower low density lipoprotein (LDL) cholesterol and supports a healthy heart. The recommended shift from saturated to unsaturated fats should occur without increasing total energy intake. One effective way to achieve this is by altering the overall dietary pattern by eating more nutrient-dense plant-based foods.
Heart disease in the UK. Over 2.3million people are living with coronary heart disease (CHD) in the UK and it is one of the leading causes of mortality with an average 180 deaths each day.
Raised blood cholesterol levels are a known modifiable risk factor for coronary heart disease (CHD). The evidence is substantial and consistently demonstrate a dose-dependent relationship between low density lipoprotein (LDL) cholesterol and the risk of CHD. Additionally, the evidence shows that lowering LDL-C reduces CHD events. The lower the LDL-C level attained, and the longer time period the reduction is maintained, the greater the clinical benefit accrued.
Over half the UK adult population have high cholesterol levels – above 5mmol/L.
Causes of elevated serum LDL cholesterol.
A main cause of elevated cholesterol levels is unhealthy dietary habits and, in particular, a high intake of saturated fatty acids. Other causes of CHD beyond genetics are also dietary related: type 2 diabetes, central obesity and metabolic syndrome.
Replacing saturated fat with unsaturated fat in the diet is central to lowering LDL cholesterol
Despite the current debate about saturated fats, 2018 saw the publication of two extensive reviews of the totality of high quality scientific evidence by the Scientific Advisory Committee on Nutrition (SACN) and the World Health Organisation (WHO). Both have concluded that lowering saturated fat and replacing with unsaturated fat will lower cholesterol levels and thus support heart health. The SACN’s and the WHO’s conclusions were in line with the earlier findings from the American Heart Association (AHA): all confirmed that saturated fat intake should be reduced but also emphasised that in order to reduce the CHD risk, saturated fat should be replaced with unsaturated fat, and especially, with polyunsaturated fat.
These findings are in agreement with the earlier conclusions of the European Food Safety Authority (EFSA) who authorised the health claim, “replacing saturated fats with unsaturated fats in the diet has been shown to lower/reduce blood cholesterol. High cholesterol is a risk factor in the development of coronary heart disease.” EFSA is responsible for assessing the scientific credibility of nutrition and health claims communicated to consumers.
The relationship between saturated fat (SFA) and CHD events is indirect, and mediated through the LDL cholesterol raising effects of dietary SFA.
Poorly designed studies have fueled the saturated fat controversy.
Studies claiming that saturated fat intakes and serum cholesterol and or CHD events are not related, have failed to take into consideration the numerous limitations of studies they have included in their review and meta-analysis process which would make any findings null and void.
- Common limitations of studies overlooked:
- Statistical power.
- The macronutrient used to replace saturated fat in the diets:
- Type of carbohydrate used to replace saturates e.g. sugars, refined carbohydrates or wholegrains. It is now well established that replacement of SFA with refined carbohydrates has no impact on CHD events or cholesterol and may even result in a negative effect.
- Confounding factors:
- Use of trans fat, particularly in older studies e.g. the Sydney Heart Study used in many of the meta-analysis fuelling the saturated fat controversy.
- Sufficient data on the range of intakes of saturated fats.
- The complexity of dietary and other changes made during interventions e.g. PUFA intakes in some studies were exceptionally high and significantly above recommendations.
- Changes in body weight when iso-energetic diets were not used between intervention groups.
- Dietary intake methodology.
- Pharmaceutical treatments (e.g. statins) in studies published after 1990.
Replacing SFA with refined carbohydrate, as many Westerners have done in an attempt to lower their total and SFA intake, has little if any impact CHD risk. Population studies failing to show lower SFA intake is associated with a lower CHD risk have failed to consider the impact of the macronutrient that replaces SFA.
The beneficial fat profile of plant-based foods (low in saturated fat, high in unsaturated fat) has been associated with lower blood LDL-C .
Beyond saturated fat for lowering cholesterol: there are other plant-based foods which have been associated with lowering serum cholesterol levels: soya protein, nuts, beta-glucans found in oats and barley as well as foods fortified with stanols and sterols.
Direct cholesterol-lowering effect of soya protein
Several meta-analysis have shown the cholesterol-lowering effect of soya protein. Soya protein seems to be capable of directly lowering LDL-C by approximately 4 to 5%. The greater the initial cholesterol level, the larger the drop in cholesterol.
Meta-analysis of clinical studies evaluating the effects of soya protein on lipid levels:
Source: Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soya protein intake on serum lipids. N Engl J Med 1995;333:276-82
One proposed explanation for the hypo-cholesterolaemic effect is that peptides formed from the digestion of soya protein upregulate LDL receptors in the liver allowing cholesterol to be removed from the bloodstream more efficiently.
This benefit of soya protein was first formally recognised by the US Food and Drug Administration (FDA) in 1999. The FDA allowed a health claim on soya foods stating that “daily consumption of 25 grams of soya protein, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease”.
In 2015, Health Canada’s Food Directorate also approved a ‘Health claim about Soya Protein and Cholesterol Lowering’. According to Health Canada’s Food Directorate, scientific evidence exists to support the health claim that consumption of soya protein helps to lower blood cholesterol levels. The Health Canada’s Food Directorate based its decision on literature research covering a period from 1980 to March 2010. All foods containing soya protein such as isolated soya protein, soya protein concentrate, textured soya protein and soya flour but also foods made from the whole soya bean are eligible for the health claim. Food containing at least 6g of soya protein per reference amount and per serving as well as complying with a list of conditions regarding the presence of recommended nutrients, maximum levels of cholesterol, alcohol, etc., are allowed to bear the health claim.
In Europe the claim has been submitted, however has not been approved for use on food products containing soya.
Indirect cholesterol-lowering effect: food substitution effect
Soya foods potentially reduce cholesterol via a combination of the direct cholesterol-lowering effect of soya protein and the substitution or displacement of higher saturated fat foods (such as fatty meat and dairy products) with soya foods providing unsaturated fats.
When soya foods replace common sources of animal protein in Western diets, which are typically high in saturated fat, the favourable change in fatty acid intake can help lower LDL-C.
Jenkins et al. explored the extent to which the displacement of animal-derived foods (high in SFA) from the diet with a soya was responsible for the cholesterol lowering properties of soya foods. Using data from 11 interventions, he calculated that when comparable amounts of animal proteins were replaced with soya proteins there was a 3.6-6.0% reduction in LDL-C due to the displacement of SFA and cholesterol from the diet.
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The UCLP© is based on the original portfolio diet by the Jenkins’ research group which involves the inclusion of four plant foods proven to lower cholesterol: soya and other plant proteins, beta-glucans from oats and barley, nuts and foods fortified with plant sterols or stanols.
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