It's time to drive a stake through the heart of a long-standing heart-health myth.
As we explained in False Advice on Fats?
, there was never good evidence that saturated fats or cholesterol cause heart disease.
And this myth – long advocated by public and private health authorities – misled Americans about the real causes of heart disease.
Replacement of saturated animal fats with partially hydrogenated (hardened) vegetable oils had two consequences:
- Hydrogenation creates trans fats – mostly omega-6s – which are proven to cause heart disease.
- This replacement created an overload of omega-6 fats, which neutralizes dietary omega-3s and fuels inflammation.
It took 50 years, but new evidence is finally alerting us to the real risk in our food supply: sugar, and sugar-like refined carbohydates.
Scientists who conducted a recent evidence review put it this way (DiNicolantonio JJ et al. 2015):
"Advice to reduce saturated fat in the diet without regard to … [differences among forms of] LDL [cholesterol], SFAs [saturated fatty acids], or dietary sources [of these nutrients] could actually increase people's risk of CHD [coronary heart disease]."
"When saturated fats are replaced with refined carbohydrates, and specifically with added sugars (like sucrose [cane sugar] or high fructose corn syrup), the end result is not favorable for heart health. Such replacement leads to changes … that may increase the risk of CHD.”
Sugar and heart disease: A brief history
Evidence that sugar-laden diets drive heart disease dates back many decades.
But those signs were ignored until saturated fats and cholesterol were exonerated.
Once saturated fat and cholesterol couldn't be blamed, the elephant in the room – America's hefty sugar habit – became apparent.
Two years ago, a population study involving 42,888 Americans revealed a very disturbing link between sugar and heart disease.
That study was conducted by scientists from the Centers for Disease Control and Prevention, Atlanta's Emory University, and Harvard.
After comparing the participants' diets to their health histories, those who consumed the most sugar were twice as likely to suffer heart attacks, compared to those with the lowest intakes.
And the government/academic team came to two other disturbing conclusions:
- Drinking one 20-oz soda daily raises your heart attack risk by about 30%.
- Your risk of heart attacks doubles if added sugars constitute 20% of your calories.
As they wrote, "Most US adults consume more added sugar than is recommended … we observed a significant relationship between added sugar consumption and increased risk for CVD mortality [death from cardiovascular disease].”
Regrettably, the U.S. Institute of Medicine still sets the recommended upper limit for added sugars at 25% of total daily calories.
In contrast, the World Health Organization (WHO) more wisely suggests no more than 10% of daily calories from added sugars.
To put these guidelines in perspective, one in 10 Americans get about 25% of their calories from added sugars, while almost three in four get 10% of their daily calories from added sugars.
In other words, most Americans are at or above the daily sugar consumption limits set by the WHO and the U.S. Institute of Medicine.
New study explains the link between sugar and heart disease
A landmark study helps explain why dietary sugar would promote cardiovascular disease.
The new findings come from California's Stanford University and Tennessee's Vanderbilt University (Shirai T et al. 2106).
In short, they found that sugar-addicted immune system cells are probably major drivers of cardiovascular disease.
Cornelia Weyand, M.D. – the paper's senior author – described the team's findings:
"We've pinpointed a defect in glucose metabolism by a class of arterial-plaque-associated immune cells as a key factor driving those cells into a hyper-inflammatory state.”
The findings support a growing recognition that chronic inflammation is a key cause of cardiovascular disease.
But, as Dr. Weyand said, "It's been unclear where the inflammation comes from.”
Inflammation drives cardiovascular disease
Cardiovascular disease arises when blood flow through the arteries that supply oxygen-rich blood to the heart is impaired.
The underlying process — the buildup of plaque inside the arteries — is called atherosclerosis.
When these deposits become severe enough, they can restrict blood flow, and create clots that block it entirely.
Fats and cholesterol are prime constituents of arterial plaque, but it also contains immune cells called macrophages.
Macrophages come into kinds:
- M1 macrophages cause inflammation as part of the body's healing and defense response.
- M2 macrophages clear cellular debris, encourage new cell growth, stimulate blood flow, and oversee tissue repair.
When the immune system detects a threat, M1 macrophages emit the unstable oxygen molecules called "free radicals”, and produce proteins that put the immune system on high-alert.
Together, these actions by M1 macrophages can result in chronic inflammation that renders the plaques increasingly brittle and prone to bursting.
If a piece of plaque suddenly breaks off it can wound the artery wall, resulting in speedy formation of clots that can trigger a heart attack, or sudden cardiac death.
Study found sugar-guzzling immune cells in heart patients
Chronic, low level, "silent” inflammation shows up in standard blood tests, such as the one for C-reactive protein, or CRP.
And having high levels of CRP usually indicates that you have high levels of an immune-signaling protein known as IL-6, that promotes inflammation and mostly comes from M1 macrophages.
Dr. Weyand's team compared macrophage cells from 140 patients with cardiovascular disease, each of whom had experienced at least one heart attack, with cells from 105 healthy but otherwise similar "control” subjects.
They discovered that cells from heart patients have a strong tendency to develop into pro-inflammatory M1 macrophages.
"We also found that macrophages from people with Type 2 diabetes, hyperlipidemia or hypertension were making more IL-6,” said Weyand.
Importantly, the more of these cardiovascular risk factors a subject had, the more IL-6 their M1 macrophages made.
Immune cells' glucose gluttony revealed as the villain
The Stanford/Vanderbilt team noticed a clue that might explain why some people are prone to cardiovascular disease.
There were twice as many free radicals inside macrophages from heart patients, compared with macrophages from healthy subjects.
They traced these free radicals to the powerhouses – called mitochondria – within the patients' macrophage immune cells.
As Dr. Weyand said. "Mitochondria inevitably wind up generating free radicals. The harder they work, the more free radicals they produce.”
When Weyand and her associates used a drug to mop up free radicals in the mitochondria of patient-derived macrophages, these cells' production of IL-6 – a major feature of their inflammatory prowess – dropped off considerably.
And this is a key point – blocking glucose metabolism within the mitochondria had the same effect.
"Something in there is leading to excessive IL-6 production,” said Weyand. "That something is our old friend sugar.”
The gluttonous appetite for glucose among the patient's M1 macrophage cells was attributed to a faulty overproduction of proteins responsible for importing glucose into cells.
"The primary problem, we learned, is that these macrophages [in heart patients] take up glucose at a higher rate than normal cells do,” said Weyand.
As she said, "That causes them to break it down faster, overheating their mitochondria, which then produce too many free radicals.”
One obvious way to reduce excess inflammatory activity in heart patients' M1 macrophage cells is by blocking glucose uptake and sponging up free radicals.
To cut cardiovascular risk, eat antioxidant-rich foods and cut back on sugar and white flour
The new study shows that some of us have M1 type macrophages with an unhealthy sugar habit.
We can't necessarily change our genetic makeup ... although there's growing evidence that diet can alter our genes' behavior.
We can all reduce our risk for cardiovascular disease – as well as heart attacks and sudden cardiac death – in two ways:
- Keep our blood sugar levels low by avoiding refined carbs and added sugars.
- Eat diets rich in fish and whole, antioxidant- and fiber-rich plant foods, to reduce free radicals, inhibit inflammation, and moderate blood sugar.
The most common added sugars are cane sugar (white or brown), molasses, honey, and high fructose corn syrup.
Cane sugar and high fructose corn syrup (HFCS) contain the same amounts of glucose and fructose.
Cane sugar consists entirely of sucrose – a molecule that's half glucose and half fructose – while HFCS ranges from 45% to 55% fructose. (Its name is misleading: it's only "high-fructose” compared with regular corn syrup.)
The major sources of added sugars in American diets are sodas, sugars, candy, cakes, cookies, pies and fruit drinks (fruitades and fruit punch); ice cream, sweetened yogurt, sweetened milk, and refined flour products (such as pastries, cookies, white breads, pasta, and the breading on fried foods).
Keep in mind that if the product has no fruit or milk products in the ingredients, all of its sugars are added sugars.
If the product contains fruit or milk products, the total sugar per serving listed on the label will include added and naturally occurring sugars.
Try these tactics to reduce sugar in your diet:
- Instead of adding sugar to cereal, add fresh or dried fruit.
- Choose sugar-free or low-calorie beverages, if you must have any*.
- Substitute unsweetened applesauce for sugar in recipes (use equal amounts).
- Remove sugar, syrup, honey, and molasses from the table: out of sight, out of mind.
- Buy fresh fruits or fruits canned in water or natural juice. Avoid fruit canned in syrup.
- Enhance foods with spices instead of sugar; try ginger, allspice, cinnamon or nutmeg.
- Try zero-calorie sweeteners such as aspartame, sucralose or saccharin in moderation*.
- Instead of adding sugar in recipes, use extracts such as almond, vanilla, orange or lemon.
- Cut back on the sugar added to things you eat or drink regularly, or use an artificial sweetener*.
- When baking cookies, brownies or cakes, cut the sugar called for in your recipe by one-third to one-half.
It's almost certainly healthier to choose foods or drinks sweetened with non-caloric alternatives such as Truvia, PureVia, Enliten, or Erylite Stevia, which contain super-sweet compounds extracted from the stevia plant (steviosides and rebaudiosides). Stevia-based sweeteners may also contain plant-derived sugar alcohols such as erythritol and xylitol, which are scarce in plants and are usually manufactured synthetically.
- DiNicolantonio JJ, Lucan SC, O'Keefe JH. The Evidence for Saturated Fat and for Sugar Related to Coronary Heart Disease. Prog Cardiovasc Dis. 2015 Nov 14. pii: S0033-0620(15)30025-6. doi: 10.1016/j.pcad.2015.11.006. [Epub ahead of print] Review.
- Shirai T, Nazarewicz RR, Wallis BB, Yanes RE, Watanabe R, Hilhorst M, Tian L, Harrison DG, Giacomini JC, Assimes TL, Goronzy JJ, Weyand CM. The glycolytic enzyme PKM2 bridges metabolic and inflammatory dysfunction in coronary artery disease. J Exp Med. 2016 Feb 29. pii: jem.20150900. [Epub ahead of print]
- Stanford University (SU). Glucose-guzzling immune cells may drive coronary artery disease. February 29, 2016. Accessed at http://med.stanford.edu/news/all-news/2016/02/excess-glucose-may-drive-coronary-artery-disease.html
- Yang Q, Zhang Z, Gregg EW, Flanders WD, Merritt R, Hu FB. Added sugar intake and cardiovascular diseases mortality among US adults. JAMA Intern Med. 2014 Apr;174(4):516-24. doi: 10.1001/jamainternmed.2013.13563.