What influences cholesterol levels
How can we reduce levels
The absorption/excretion circulation pathways, highlighted above, highlight how raised serum levels are complex and influenced by a host of genetic, environmental, dietary and biological factors.
Lack of physical activity
Cholesterol is an excellent energy source, especially for individuals participating in regular exercise. Exercise has been shown not only to help weight control but also to lower serum triglycerides, total cholesterol and improve the ratio of high-density lipoprotein to low-density lipoprotein. Furthermore, there is evidence, that even before weight reduction occurs, exercise directly lowers excess serum testosterone, oestrogen and leptin levels and raises adiponectin levels, all of which have an effect on cholesterol pathways. Try to be physically active throughout the day (use the stairs instead of the lift, get off the bus or tube one stop earlier, choose to walk or cycle rather than use the car etc.). It’s important to avoid long periods of sedentary behaviour and prioritise time to introduce a formal workout 2-4 times a week – tips to increase exercise levels.
Excess dietary cholesterol and saturated fat intake
Eating large quantities of cholesterol-rich animal products when you don’t need the calories overloads the body and forces it to store this extra cholesterol in locations such as the liver and arteries, increasing serum levels. Since animal cells manufacture cholesterol, all animal-based foods contain cholesterol in varying amounts. Likewise, saturated fats contain a lot of energy, and if this energy is not required, the body is forced to improvise and find ways to store this excess triglyceride and cholesterol. Plant oils can contain saturated fats, but these are not harmful and certainly don’t share the problems found with meat fats.
Foods high in saturated fats and cholesterol include
- Butter, lard
- Pies, cakes
- Fatty cuts of meat, sausages, bacon
- Cheese, cream and products made with them
- Shrimp and lobster
Higher intake of transfats
These are man-made in a process in which unsaturated vegetable oils are partially hydrogenated to produce saturated fats. This alters the melting point and freezing points, making them useful for margarine, snack foods, packaged baked goods and frying fast food. Apart from energy, trans-fats have little nutritional value and, by raising levels of LDL and lowering HDL, have been consistently shown to be associated with an increased risk of heart disease. Fortunately, awareness of their health risks and pressure on the food industry is reducing their use.
Low intake of polyunsaturated fats
Several studies, including a meta-analysis by Cambridge University, have found an association between higher intake of both omega-3 and 6 fats and significantly reduced risk of heart disease and lower cholesterol (LDL). A scientific report from the American Heart Association has also found a favourable link between lower cholesterol (LDL) and higher dietary omega 3 & 6 polyunsaturated fat intake.
Short-chain omega 3, consisting of alpha-linolenic acid (ALA) and eicosatetraenoic acid (ETA), is found in walnuts, edible seeds, clary sage, algal oil, flaxseeds and flaxseed oils, sacha inchi, echium and hemp oils. Long-chain omega 3, consisting of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are found in algae, edible seaweed, phytoplankton, oily fish such as herring, mackerel, salmon, menhaden and sardine, as well as cod liver, squid, krill oils and other marine foods. DHA is the primary structural component of the human brain, skin and retina.
Most omega-6 fatty acids originate from vegetable oils, nuts, grape seed oil, soya, flaxseed and oily vegetables such as avocado. Linoleic acid, the shortest-chained omega-6 fatty acid, is essential because the human body cannot synthesise it. The other omega 6’s can occur in smaller amounts in various and include gamma-linolenic acid (GLA), Di Homo gamma linoleic acid (DGLA) and Arachidonic acid (AA). These omega 6’s are generally synthesised by the body.
The trouble with a typical western diet is that is becoming increasingly low in omega 3, in part because the animals we eat are rarely able to roam free and eat a varied diet. As a consequence, the ratio of omega 3 to 6 consumption is changing to 10-20:1, when ideally it should be 3-4:1. The best way to improve this ratio is to eat oily fish 2-3 times a week as part of a regular balanced diet.
Sources of polyunsaturated fatty acids include…
Fish: Fish: The most widely available source of unsaturated fats and essential long-chain n-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) is cold-water, oily fish. Interestingly, fish do not synthesize them; they obtain them from the algae and plankton they eat. Fish with the highest levels include mackerel, salmon, herring, anchovies, pollock, shark, swordfish, sardines and, to a lesser extent, tuna. These fish have around seven times as much n−3 as n−6. Consumers of oily fish should be aware of the potential presence of heavy metals such as mercury and cadmium (from discarded batteries), as well as chemicals such as dioxin. As these accumulate in the food chain, larger fish such as shark and swordfish have the highest levels. It is suggested that their intake should be limited to twice a week (which is still more than the majority of people currently consume in a western diet). However, after an extensive review of the evidence, Harvard’s School of Public Health reported in the Journal of the American Medical Association that the benefits of fish intake generally far outweigh the potential risks. Contamination is even lower in white, sea fish such as bass and bream, and no limits have been set on their consumption, although these have lower omega 3 levels. Freshwater fish such as trout and lake varieties are almost completely free of potential heavy metal contamination and have good levels of omega 3. Some protection from mercury contamination can be gained from eating foods rich in selenium (brazil nuts, crab meat), as this metal can bind to the mercury and stop it being absorbed into the body.
Linseeds (flax seeds) and the healthy oil it produces have a very high percentage of unsaturated to saturated fats. It also contains a high percentage of omega-3 content, six-times richer than most fish oils, albeit in the short-chain form (alpha-linoleic acid).
Avocado has the highest oil content of all fruits, and most of its fats are unsaturated, monounsaturated and omega-9. Other natural sources of healthy fats include rapeseed oil, which is particularly cheap as it can be grown in northern European countries.
Nuts almost all contain a good percentage of unsaturated fats. Walnuts are one of few nuts that contain appreciable omega-3, with the ratio between omega 3 and 6 being approximately 1:4.
Kiwi fruit has an even better ratio of omega 3-6, but there are only small quantities of oil in kiwi’s as opposed to linseeds.
Microalgae are rich sources of the longer-chain omega-3 fatty acids (EPA and DHA) and can be produced commercially in bioreactors. This is the only source of DHA acceptable to vegans. Brown algae (kelp) is also an excellent source of EPA.
Other plant-based foods with a good ratio of omega 3-6 include acai, seaweed, butternuts, chai sage, shiso and lingonberry. The leafy green vegetable Portulaca oleracea (Purslane) has the highest omega 3 levels of green vegetables but is very rarely used in western cooking. Some vegetables contain a small amount of omega 3, notably strawberries and broccoli.
Extracted plant oils used for cooking or salads contain a mixture of saturated and unsaturated fats. Linseed (flax seeds), olive and rapeseed (canola) oils have a particularly good percentage of unsaturated fats. Sunflower, soya bean and corn oil all contain mostly polyunsaturated fats, but tend to be heavily processed during manufacturing. Palm and coconuts have the highest percentage of saturated fats, making them energy-rich and potentially unhealthy, although cold-pressed varieties can still be healthy. In terms of the omega 3-6 ratio, the best oils are linseed, rapeseed, soybean and olive (which also has omega-9). Oils from microalgae and kelp contain the highest DHA and EPA levels and are usually taken as a supplement rather than used for cooking. Sunflower, palm kernel, cottonseed, grapeseed and corn oil contain virtually no omega-3.
In regard to meat, if you have high cholesterol, lower your intake and buy grass-fed animals, particularly game. Chickens which roam around eating grass, worms and insects, as well as grain, generally have much higher omega-3.
Eggs can be a good source of omega 3 (mostly ALA) and protein, but only if produced by chickens fed a diet of greens and insects rather than corn or soybeans. In addition to feeding chickens insects and greens, fish oils may be added to their diet in order to increase fatty acid concentrations in eggs. The addition of flax, chia and canola seeds to the diet of chickens, both good sources of alpha-linolenic acid, increases the omega-3 content of eggs, yet is very rarely done for mass-produced chicken eggs.
Milk and cheese from grass-fed cows may also be good sources of omega-3. One UK study showed that half a pint of milk from grass feed cows provides 10% of the recommended daily intake (RDI) of ALA, while a piece of organic cheese may provide up to 88%.
Higher processed sugar intake
A number of cohort studies have linked higher processed sugar intake with higher serum cholesterol and heart disease. Notwithstanding the influence of sugars on obesity, the two explanations behind why sugar increases cholesterol are, firstly, that the peaks and troughs of insulin levels it creates signal the body’s metabolism into believing it needs to store more energy, thus decreasing excretion of cholesterol and increasing reabsorption. The second explanation is that sugar leads to increased expression of inflammatory markers, including 12-lipoxygenase (12-LOX) and its arachidonate metabolites (see below). The most convincing study, published in the Journal of the American Medical Association, analysed the dietary habits of a cohort of 6110 Americans and showed that, after several years, those who ate more than 10% of their daily calories as sugar had significantly raised triglyceride levels, lower HDL and higher LDL cholesterol levels – tips to reduce processed sugar intake.
Not having a healthy gut bacterial flora
Research presented at the American Heart Association’s Scientific Sessions reported that a formulation of Lactobacillus may be able to reduce blood levels of LDL (bad cholesterol). A total of 60 people between the ages of 18-65 took part in the randomised, double-blind, placebo-controlled study. The group taking the probiotic strains experienced, on average, reductions in total cholesterol levels of 13.6%. Probiotic bacteria reduce cholesterol by producing significant levels of bile salt hydrolase, which is effective at metabolising bile salts that contain cholesterol. These strains are also able to incorporate dietary fat into their bacterial cellular surface, reducing the absorption of saturated fat – more about good quality probiotics. Apart from a good probiotic supplement, healthy bacteria can be found in:
- Miso Soup
- Other fermented cabbage foods
Dietary phytochemicals and polyphenols
Numerous cohort studies have linked higher intake of polyphenol-rich foods with lower total cholesterol, LDL and heart disease. As well as lowering the risk of heart disease, these natural chemicals also have numerous health benefits, particularly in the reduction of chronic diseases which affect humans including diabetes (read more), dementia, arthritis (read more) and Parkinson’s disease. Foods with high polyphenol content include:
- Leafy green vegetables
- Cruciferous vegetables
- Chocolate (unsweetened of course)
- Herbs and spices
Phytosterols are structurally related to cholesterol. Plants manufacture phytosterols, which compete with cholesterol for reabsorption in the intestinal tract, thus reducing cholesterol reabsorption. When intestinal lining cells absorb phytosterols, in place of cholesterol, they usually excrete the phytosterol molecules back into the gut, an important protective mechanism. Sitosterol and campesterol are the most frequent plant sterols and constitute about 60% and 35% respectively of plant sterols in food. Plant stanols, are the saturated form of plant sterols, meaning they have no double bond in the sterol ring. Saturated sitosterol is known as sitostanol, and saturated campesterol is campestanol. Plant foods that are particularly rich in phytosterols (stanol or sterol esters) include:
- Soy beans
- Pumpkin seeds,
- Grains, vegetables, fruits, nuts and seeds
Regular intake of these foods is linked to lower serum cholesterol levels, as highlighted in a recent meta-analysis of 41 trials which highlighted how 2-3 g of phytosterols per day reduced low-density lipoprotein (LDL) by about 10%. The beneficial effects were also found to be additive when combined with other lifestyle interventions. For example, eating foods low in saturated fat and cholesterol and high in phytosterols reduced LDL by up to 20%, while eating them with statin medication almost doubled their cholesterol-lowering capacity.