The Relationship Between the Glycemic Load, Glycemic Index of Food and Blood Sugar to the Development of Heart Disease

Almost everyone knows that processed sugar often leads to the development of diabetes. Some people are lucky and can eat all the sugar they want without getting diabetes. My parents are an example. I recently visited them and was amazed at how much sugar they were eating. My father would substitute dinner for three chocolate bars and ice cream. Since he is unlikely to develop diabetes at this point, I had to come up with another reason to get him to cut back on his sugar intake. I was thinking about telling him to switch to sugar-free snacks, but I remembered that these snacks often substituted fat for sugar and were therefore more calorie dense (fat contains more calories per gram than sugar). This could lead to weight gain and increase his risk for problems related to obesity.

After this, I wondered if sugar intake could cause heart disease in the absence of diabetes. Surprisingly, there is not much research in this area. This is what prompted me to write this blog. Is sugar intake related to heart disease? Since there is such little research on this topic, I decided to see if there is a relationship between the glycemic load of food and heart disease. This question had much more research available. Before I get to the research, I will first explain what the glycemic load of food actually is.

What is the glycemic load of food?

I am sure a lot of you are familiar with the glycemic index of food. The glycemic index refers to the carbohydrate content of a food and how it affects our blood sugar. The problem with this is that it does not take into account the portion size of the food usually eaten. An example is watermelon, which has an extremely high glycemic index. This index corresponds to a portion larger than what is usually eaten, so the actual glycemic index would be lower. This is a problem because it may scare people away from eating certain fruits with a high glycemic index.

To address this problem, scientists came up with the glycemic load. The glycemic load takes into account the glycemic index plus the amount of carbohydrates in the food typically eaten. Let’s go back to watermelon. Watermelon has a high glycemic index but a low glycemic load. But why? The answer is because watermelon has such few calories and, hence, few carbohydrates. It is made mostly of water (duh). You would likely have to eat close to a whole watermelon to cause the rapid spike in your blood sugar represented by the glycemic index.

The relevance of glycemic load and glycemic index to health is based on the assumption that frequent and rapid spikes in blood sugar lead to diabetes by overproducing insulin in reaction to all the sugar in the blood. After a while, the cells become less responsive to insulin because it is always excreted in abundance. When cells are less responsive, sugar does not enter the cells but instead stays in the bloodstream, where it causes various health problems.

Studies looking at the relationship between glycemic load and blood lipids

•  Blood lipids- HDL (good cholesterol), LDL (bad cholesterol) and triglycerides; changing the amount and ratio of HDL & LDL cholesterol can increase risk of cardiovascular disease.
•  Blood lipids are often looked at to estimate the risk of cardiovascular disease.

One large study involving over 18,000 women over the age of 45 and without diabetes found an association between the glycemic load of the diet and blood lipids (1). The changes in HDL/LDL ratio, HDL levels, and triglyceride levels associated with a high glycemic load diet appear small, but they are significant. The change in HDL cholesterol between the lowest and highest glycemic load groups results in a 22% increase in the risk of heart disease; the change in HDL/LDL ratio amounts to a 14% increase, while the change in triglyceride levels increases the risk of heart disease by 7%.

How blood glucose levels can affect blood lipids

• Blood lipids refer to HDL (good cholesterol), LDL (bad cholesterol) and triglycerides which are found in our blood
• Glucose is a simple sugar which our body uses for energy-when we say blood sugar levels we mean levels of glucose in our blood
•  Blood lipids are often looked at to estimate the risk of cardiovascular disease

There is a theory about how raised blood glucose levels would lead to an unfavorable blood lipid profile (HDL, LDL, and triglycerides). It is believed that following a meal that produces a spike in blood sugar, hours later blood sugar may drop significantly (likely from overproduction of insulin), leading to hypoglycemia (low blood sugar) (1). When hypoglycemic, the body may respond by releasing hormones that increase the concentration of glucose and free fatty acids. This reaction, combined with increased insulin production, often leads to insulin resistance.

Researchers believe that insulin resistance leads to an increase in triglyceride levels and inflammatory markers while causing a decrease in HDL (good cholesterol). It may also cause oxidative stress, which increases inflammation. The problem I have with this theory is that if someone could eat sugar without ever becoming insulin resistant, they would be immune to negative changes in blood lipid levels and inflammatory markers.

Glycemic load, glycemic index, C-reactive protein and cardiovascular events

Scientists conducted a large study involving 75,000 women without known cardiovascular disease and followed up with the subjects for 10 years, during which time they looked for a link between the glycemic load and glycemic index of a diet and the risk of cardiovascular disease (2). They found that a high-glycemic index diet was strongly associated with an increased risk of cardiovascular disease. They also found a similar association between glycemic load and cardiovascular disease in women with a BMI > 23, but little relation in women with a BMI < 23.  (BMI is a measure to tell if someone is of normal weight, overweight, or obese.).

A large Italian study involving 15,000 men and 30,000 women measured whether or not glycemic index and load were related to coronary heart disease (3). They found that a diet high in glycemic index and eating carbohydrates with a high glycemic index increased the overall risk of cardiovascular disease in women but not in men. Although there have only been a few prospective studies on this issue, the majority have found that high glycemic index and glycemic load diets increase the risk of cardiovascular disease in women but not in men.

Lastly, a Danish study involving 15,000 middle-aged women found that moderate and high-glycemic-load diets were associated with an increased risk for cardiovascular disease (4). The effect of glycemic load on cardiovascular disease was stronger in overweight women. In fact, most of the studies I talked about have found that being overweight increased the negative effect of a high-glycemic load diet on cardiovascular disease.

There is a scientific explanation that may shed light on why the bodies of men and women react differently to high-GI and high-GL foods, which I will get to shortly.

Relationship between glycemic load and C-reactive protein

•  C-reactive protein is a measure of inflammation- higher levels indicate more inflammation
•  Ischemic heart disease- when blood supply to the heart is reduced (narrowed by plaque) and it may not receive enough oxygen

A recent study involving 244 healthy women examined the relationship between dietary glycemic load and levels of C-reactive protein, an inflammatory marker for ischemic heart disease (5). Previous studies have shown that levels of C-reactive protein are associated with the development of ischemic heart disease. The researchers found that as dietary glycemic load increased, so did levels of C-reactive protein, in an almost perfectly linear fashion (as one variable goes up, so does the other). When women were separated into five groups based on the increasing glycemic load of their diets, it was found that the median concentrations of C-reactive protein were 1.9, 2.1, 3.2, 2.8, and 3.7 mg/L, respectively (as the glycemic load of each group increased, so did the C-reactive protein levels). A high dietary glycemic load may increase the risk of ischemic heart disease through its effect on the pro-inflammatory marker C-reactive protein.

Proposed explanation for why men and women differ in response to GI and GL foods

Theories in science are never the end-all explanation for events. Theories are always being updated and changed with the discovery of new information. Scientists can only make theories with the information they currently have. When hearing a theory, you should not automatically take it as the final word on a subject. Having healthy skepticism is key to advancing theories.

Scientists have discovered that women metabolize lipoproteins (HDL, LDL, and VLDL) roughly twice as fast as men. This means that women break down the lipoprotein and absorb it twice as fast as men. Compared to men, when women eat dietary fat and carbohydrates, they experience a greater increase in triglyceride levels, a decrease in HDL cholesterol, and smaller increases in LDL cholesterol.

Hyperglycemia (high blood glucose levels) and risk of Cardiovascular Disease

•  Glucose is a simple sugar which our body uses for energy-when we say blood sugar levels we mean levels of glucose in our blood

It has been well documented that diabetes leads to plaque in the heart due to excessive sugar damaging blood vessels. So far, studies have produced inconsistent results when looking at levels of blood glucose, which do not fall under diabetes but may still damage blood vessels and lead to plaque deposits in the heart. To help clarify this issue, a meta-analysis looked at 38 studies that examined the relationship between high blood glucose levels following the intake of carbohydrates and the risk of cardiovascular disease (6).

The researchers found that those in the category with the highest blood glucose levels had a cardiovascular disease risk that was 36% greater than those in the lowest blood glucose level category (6). The link between high blood glucose and cardiovascular disease was stronger in women and mixed-sex studies than in men-only studies. Randomly taken blood glucose levels were also strong predictors of cardiovascular disease. There was a positive association between post-challenge blood glucose levels (you eat a known amount of glucose and they measure your blood sugar an hour later) and the risk of cardiovascular disease; as the blood glucose level increased, so did the risk for cardiovascular disease.

How excessive sugar in the blood can affect the heart

When blood sugar is not controlled, the excess glucose in the blood can cause damage to nerves and blood vessels. This is the reason that diabetes causes blindness, loss of limbs, kidney failure, and cardiovascular disease. We are not supposed to have extra glucose just hanging around in our blood. It should be stored or sent to cells that need it. How the blood vessels become damaged is not completely understood, but it is likely complex and involves the effect of glucose on other molecules like proteins and fats.

When blood vessels are damaged, our body deposits cholesterol to prevent further damage to the blood vessels. When cholesterol accumulates, the blood vessels become narrower, restricting blood flow and leading to the hardening of the arteries.

 Discussion

The majority of studies conducted looking at a link between a high glycemic load diet and cardiovascular disease used middle-aged women. It seems a high-glycemic-load diet increases the risk of cardiovascular disease in women more than men, especially for overweight women. The results for men are less consistent, although many studies have found a correlation.

I know this blog was a bit more technical than past blogs. I always try my best to make everything easy to understand for everyone, but sometimes this is not possible without sacrificing important information about a topic. I will summarize the main findings to help you better understand this blog. If you are still confused about certain parts, please email me or leave a comment.

1. Studies have shown that high blood sugar levels in people with diabetes lead to heart disease; the sugar in the blood (where it should not be) causes damage to blood vessels and nerves.
2. I wanted to know if eating a high-glycemic load diet (a measure of how much a food raises blood sugar) can cause heart disease in people without diabetes.
3. It appears that a high-glycemic-load diet can increase the risk of cardiovascular disease in men and women, although the association is stronger in women.
4. A high-glycemic load diet increases levels of C-reactive protein, a protein used as an indicator of inflammation.
5. Theoretically, any extra sugar hanging around in our blood can begin to damage nerves and blood vessels; we just have not found out at what level blood sugar starts to become dangerous.

In conclusion, even without having diabetes, eating a diet that causes rapid spikes in blood sugar can lead to cardiovascular disease. I have attached a chart showing the glycemic index and glycemic load of various foods.

FOOD	Glycemic index (glucose = 100)	Serving size (grams)	Glycemic load per serving
BAKERY PRODUCTS AND BREADS
Banana cake, made with sugar	47	60	14
Banana cake, made without sugar	55	60	12
Sponge cake, plain	46	63	17
Vanilla cake made from packet mix with vanilla frosting (Betty Crocker)	42	111	24
Apple, made without sugar	48	60	9
Bagel, white, frozen	72	70	25
Hamburger bun	61	30	9
White wheat flour bread	71	30	10
Whole wheat bread, average	71	30	9
Corn tortilla	52	50	12
BEVERAGES
Coca Cola, average	63	250 mL	16
Apple juice, unsweetened, average	44	250 mL	30
Cranberry juice cocktail	68	250 mL	24
Orange juice, unsweetened	50	250 mL	12
BREAKFAST CEREALS AND RELATED PRODUCTS
Cornflakes, average	93	30	23
Grapenuts, average	75	30	16
Oatmeal, average	55	250	13
Special K (Kellogg’s)	69	30	14
GRAINS
Quinoa	53	150	13
White rice, average	89	150	43
Brown rice, average	50	150	16
COOKIES AND CRACKERS
Graham crackers	74	25	14
Vanilla wafers	77	25	14
Rice cakes, average	82	25	17
Rye crisps, average	64	25	11
Soda crackers	74	25	12
DAIRY PRODUCTS AND ALTERNATIVES
Ice cream, regular	57	50	6
Ice cream, premium	38	50	3
Milk, full fat	41	250mL	5
Milk, skim	32	250 mL	4
Reduced-fat yogurt with fruit, average	33	200	11
FRUITS
Apple, average	39	120	6
Banana, ripe	62	120	16
Dates, dried	42	60	18
Grapefruit	25	120	3
Grapes, average	59	120	11
Orange, average	40	120	4
Peach, average	42	120	5
Pear, average	38	120	4
Raisins	64	60	28
Watermelon	72	120	4
BEANS AND NUTS
Baked beans, average	40	150	6
Black beans	30	150	7
Kidney beans, average	29	150	7
Lentils, average	29	150	5
Soy beans, average	15	150	1
Cashews, salted	27	50	3
Peanuts, average	7	50	0
PASTA and NOODLES
Fettucini, average	32	180	15
Spaghetti, white, boiled 20 min, average	58	180	26
Spaghetti, wholemeal, boiled, average	42	180	17
SNACK FOODS
Corn chips, plain, salted, average	42	50	11
Fruit Roll-Ups	99	30	24
M & M’s, peanut	33	30	6
Potato chips, average	51	50	12
Pretzels, oven-baked	83	30	16
Snickers Bar	51	60	18
VEGETABLES
Green peas, average	51	80	4
Carrots, average	35	80	2
Baked russet potato, average	111	150	33
Sweet potato, average	70	150	22
Yam, average	54	150	20
Honey, average	61	25	12

Sources

1. Levitan, E. B., Cook, N. R., Stampfer, M. J., Ridker, P. M., Rexrode, K. M., Buring, J. E., … & Liu, S. (2008). Dietary glycemic index, dietary glycemic load, blood lipids, and C-reactive protein. Metabolism, 57(3), 437-443.
2. Liu, S., Willett, W. C., Stampfer, M. J., Hu, F. B., Franz, M., Sampson, L., … & Manson, J. E. (2000). A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. The American Journal of Clinical Nutrition, 71(6), 1455-1461.
3. Sieri, S., Krogh, V., Berrino, F., Evangelista, A., Agnoli, C., Brighenti, F., … & Panico, S. (2010). Dietary glycemic load and index and risk of coronary heart disease in a large italian cohort: the EPICOR study. Archives of Internal Medicine, 170(7), 640-647.
4. Beulens, J. W., de Bruijne, L. M., Stolk, R. P., Peeters, P. H., Bots, M. L., Grobbee, D. E., & van der Schouw, Y. T. (2007). High dietary glycemic load and glycemic index increase risk of cardiovascular disease among middle-aged women: a population-based follow-up study. Journal of the American College of Cardiology, 50(1), 14-21.
5. Liu, S., Manson, J. E., Buring, J. E., Stampfer, M. J., Willett, W. C., & Ridker, P. M. (2002). Relation between a diet with a high glycemic load and plasma concentrations of high-sensitivity C-reactive protein in middle-aged women. The American journal of clinical nutrition, 75(3), 492-498.
6. Levitan, E. B., Song, Y., Ford, E. S., & Liu, S. (2004). Is nondiabetic hyperglycemia a risk factor for cardiovascular disease?: a meta-analysis of prospective studies. Archives of internal medicine, 164(19), 2147-2155.