Do you often wonder why health advice often appears to be the same for various conditions? ‘Lose weight, eat more vegetables, exercise more’ – we all know it’s good for us, yet why are we facing an ever-growing health crisis?
The stats show that while up to 40% of adults in Western countries have high cholesterol, most people aren’t doing anything about it,. It’s clear, then, that the key message still isn’t getting through as clearly as it ought.
However, by exploring the science behind the advice, we hope to highlight that the power is in your hands.
Read on for the full low-down on the how, what and why behind the guidelines.
Exercise and cholesterol management
We all know that exercise is good for us, but it appears to be particularly potent when it comes to managing our cholesterol and improving blood lipid levels.
1. Exercise supports cholesterol and lipoprotein clearance
Research shows that people who perform more exercise have higher high-density lipoprotein (HDL) levels, a lipoprotein that promotes healthy cholesterol levels.
Low-density lipoproteins transport cholesterol to cells for use in plasma membranes and producing steroid hormones. Excess cholesterol is removed from cells by HDL and returned to the liver through a process known as ‘reverse transport’. It then is either recycled or stored as bile in the gall bladder.
Research shows that exercise boosts the reverse transport process, effectively increasing HDL’s ability to catch and recycle excess cholesterol,.
2. Exercise improves insulin sensitivity
Exercise can also benefit your blood lipids by improving insulin sensitivity. Insulin’s role is to shuttle nutrients to cells, such as proteins and glucose (the broken-down form of carbohydrates).
Insulin resistance occurs when cells in your muscles, body fat, and liver begin to resist or ignore the signal being emitted by insulin, i.e. to uptake glucose from the blood and store it.
The body fights back by producing more insulin, but the pancreas’ beta cells become worn out over months and years and cannot keep up with the increasing demands for insulin. Blood sugar levels rise as a result, and you may develop pre-diabetes or type 2 diabetes.
It is also important to note that insulin resistance is a hallmark of a cluster of diseases known as ‘metabolic syndrome’, including obesity, high blood pressure, high cholesterol and type 2 diabetes, all of which significantly increase the risk of all-cause mortality.
Insulin resistance impacts blood lipids by increasing low-density lipoproteins (LDL) and triglycerides, which are produced from dietary fat in the liver,. Triglycerides cannot combine with fluids and therefore ‘piggyback’ onto lipoproteins to travel through the blood.
As a result, if the liver produces more triglycerides, you need more VLDL and LDL to transport them to target tissues.
When circulating levels of low-density lipoproteins increase, they become more likely to enter and accumulate behind the arterial walls. This results in the development of plaques, which block the circulatory system, a process known as atherosclerosis.
Fortunately, research shows that regular physical activity significantly improves insulin sensitivity and helps reverse these negative impacts on blood lipids,,. More intense forms of exercise, such as resistance training, appear to be even more effective at increasing insulin sensitivity, meaning they may have the most powerful impact on reversing the adverse effects of insulin resistance on blood lipids.
Weight loss and cholesterol management
Obesity is a key risk factor for high cholesterol. Obese individuals typically have lower HDL and higher LDL and triglyceride levels when compared to those at a healthy weight. Independent of lifestyle factors like diet and exercise, obesity seems to cause adverse changes that impact blood lipids, including:
1. Impaired fat metabolism
When we digest fats, the lipids absorb into the intestinal cell wall, where they are packaged into chylomicrons to be transported around the body. These transport lipids from the intestines to the liver, from which VLDL transports triglycerides to cells for use as energy or stored in fat tissue.
However, obesity means that the body becomes less efficient at metabolising and breaking down triglycerides, resulting in elevated levels of low-density lipoproteins circulating through the blood. Under normal circumstances, these tissues would be able to update these compounds, but insulin resistance means they do not effectively respond to insulin’s signal.
2. Systemic inflammation
Obesity goes hand-in-hand with systemic inflammation, a non-specific immune response that damages the body’s tissues. This can cause the arterial walls to remodel and make it easier for plaques to develop in the vascular system.
3. Increased production of precursors to LDL
Obesity and insulin resistance cause an increase in the production of precursors to LDL, including the enzyme lipoprotein lipase. This compound decreases the density of lipoproteins, meaning they are more likely to become trapped behind arterial walls, causing a build-up of plaque.
Fortunately, evidence suggests that modest weight loss of just 5% from baseline is enough to improve cholesterol and lipoprotein levels. A significant contributing factor is that a caloric deficit and weight loss enhances insulin sensitivity. Equally, weight loss also correlates with improved lifestyle habits, such as diet and exercise patterns, which have independent positive impacts on blood lipids.
Dietary choices and cholesterol
While evidence shows that dietary cholesterol intake is not a significant problem, there’s no doubt that nutrition plays a key role in managing cholesterol levels.
Excess intake of saturated fats, generally found in animal products like high-fat dairy or meat, and trans fats, increase total cholesterol and LDL levels. One of the main theories behind the impact of fats on lipoproteins is their influence on how the body metabolises fats or triglycerides.
The body uptakes lipoproteins from the blood at ‘receptor sites’, located in muscle cells, adipose tissue, and other cells. The ‘activity’ of this receptor site refers to how well these lipids attach to their receptor site, whereas their ‘abundance’ refers to how many sites there are in a specific tissue or organ. The greater the abundance, the bigger the likelihood that a substance can bind to the receptor site, preventing excess lipids from circulating in the blood.
It appears that fat saturation levels specifically reduce LDL receptor site abundance and activity. This means that when you eat a diet high in saturated fat, your body can’t remove LDL from circulation as effectively. As a result, these low-density lipoproteins accumulate and penetrate the arterial walls more readily and become trapped. However, replacing saturated and trans fats with unsaturated fats reduces total cholesterol, increases HDL, decreases LDL levels, and lowers triglycerides.
Likewise, trans fats (TFAs), often found in processed baked goods and fried foods, also appear to be particularly harmful through three mechanisms.
1. TFAs reduce the size of lipoprotein particles
Smaller lipoproteins can enter arterial walls more readily and accumulate to form plaques.
2. TFAs reduce lipoprotein’s efflux capacity
When lipoproteins cannot effectively efflux (clear) excess cholesterol and lipoproteins, it results in higher levels of circulating cholesterol lipoproteins, which become more likely to penetrate and become stuck behind arterial walls.
3. TFAs decrease HDL and increase LDL and VLDL.
With lower HDL levels and higher amounts of LDLs circulating, the body becomes less able to efflux cholesterol.
In addition, TFA intake generally correlates with other risk factors for cardiovascular diseases, like inflammatory biomarkers and endothelial dysfunction. The endothelium is the lining of the cardiovascular system, which acts to protect and secrete important substances like nitric oxide. Excessive intake of compounds such as TFAs can result in vascular remodelling that means your arteries accumulate plaque more rapidly.
High sugar intake appears to correlate with elevated LDL levels and low HDL levels. Experts theorise that sugars play a negative role due to their contribution to insulin resistance. Even where calorie intake is equal, high-sugar diets result in increased insulin levels and impaired insulin sensitivity compared with diets rich in complex and fibrous carbohydrates. Therefore, even if you are not overweight, high amounts of sugar and low intakes of fibre can impact blood lipids similarly to other factors that cause insulin resistance, like obesity and chronic inactivity.
A secondary impact is that high-sugar foods tend to be cheap and highly calorific, meaning they often go hand-hand with weight gain and obesity. However, it’s important to note that this connection is often due to positive energy balance, resulting in excess body fat. However, because obesity has several negative impacts on blood lipid metabolism, a high-sugar diet is a double whammy when maintaining healthy cholesterol levels.
In contrast to added sugars, a high intake of fibre appears to reduce LDL and total cholesterol. Specifically, there are two types of dietary fibre: soluble and insoluble. Of the two, soluble fibre, commonly found in oats and legumes, seems to have the most significant impact on lowering LDL.
Soluble fibre dissolves in water to form a gel-like substance and picks up fat, dietary cholesterol, bile salts, and sugar for excretion as it moves through the gut. After these products have been cleared, they are no longer available to produce more cholesterol. Another mechanism through which fibre improves cholesterol levels is its ability to reduce excessive blood sugar increases after eating. When blood sugar levels are high, more triglycerides are present, thereby increasing cholesterol production.
A final benefit of high-fibre diets is their positive influence on blood sugars and insulin sensitivity. Numerous studies have demonstrated that high dietary fibre intake improves insulin resistance and the risk of developing type 2 diabetes. And not only does fibre reduce LDL levels through its positive effect on glucose metabolism, but it also increases the production of HDL. So, while there are many reasons to eat your five-a-day, cholesterol management is a particularly important factor.
Modern technology means we now have more access than ever to health advice, and cholesterol is no exception. But because this guidance often fails to explain exactly how and why each element is important, the importance of the core message may become lost. While it remains the case that lifestyle choices such as exercise, diet and weight management are crucial factors, understanding the ‘why’ behind the advice may be the key to improving their application.
- Exercise helps improve blood lipids by enhancing insulin sensitivity and boosting ‘reverse transport’.
- In obese individuals, weight loss improves lipid metabolism, insulin sensitivity and reduces LDL production.
- Replacing saturated and trans fats in the diet with more unsaturated fat increases HDL while reducing LDL and lowering triglycerides.
- Replacing added sugar with complex and fibrous carbohydrate sources can help improve insulin sensitivity, reverse the negative impact of obesity on blood lipids, and increase the disposal of excess cholesterol and lipoproteins.