|Insulin Resistance Syndrome|
The insulin resistance syndrome (IRS) is a group of health risk factors that increase the likelihood of heart disease,1 2 3 4 and perhaps other disorders, such as diabetes and some cancers.5 6 The risk factors that make up IRS include insulin resistance, which refers to the reduced ability of the hormone insulin to control the processing of glucose by the body. Other major risk factors often associated with IRS include high blood sugar and high blood triglycerides, low HDL (“good”) cholesterol, high blood pressure, and excessive body fat in the abdominal region. People with IRS do not always have every one of these risk factors, but they usually have many of them. A qualified doctor should make the diagnosis of IRS after a thorough examination and blood tests.
Most people with type 2 diabetes have insulin resistance, but many more people who are not diabetic also have insulin resistance.7 8 9 Since insulin resistance itself often does not cause symptoms, these people may not be aware of their problem. Some authorities believe insulin resistance is partially inherited and partially due to lifestyle factors.
In addition to the recommendations discussed below, people with IRS may benefit from some of the recommendations given for type 2 diabetes. People with IRS should also benefit from health strategies that reduce the severity of the risk factors they possess, including obesity, high triglycerides, and high blood pressure.
What are the symptoms of insulin resistance syndrome?
People with IRS may be overweight (especially in the trunk area), feel sluggish after eating, and may have been told that they have high blood pressure and high cholesterol.
Dietary changes that may be helpful for insulin resistance syndrome
Some authorities recommend people with IRS avoid high-carbohydrate diets, and some recommend a diet lower in carbohydrate than current public health guidelines suggest. The rationale is that high carbohydrate intake stimulates increased insulin levels, which can lead to high triglycerides, low HDL, and other adverse changes in the levels of blood fats that contribute to heart disease risk.10 Other authorities disagree, however, because they believe a lower carbohydrate diet will result in higher calorie intake from fat, leading to more difficulties with overweight, insulin resistance, and heart disease risk.11 A recent preliminary study suggested that a healthy, balanced diet low in fried foods and sausages, and high in vegetables, fruits, fish, and complex carbohydrates, such as whole grain rice and pasta, was associated with protection from many aspects of IRS.12
The effect of dietary fat on insulin resistance seems to depend on the type of fat eaten. Preliminary studies in animals and humans suggest that insulin resistance is worsened with increased use of saturated fat and improved with increased unsaturated omega-3 fatty acids from fish, while the role of other unsaturated fats is less clear.13 However, recent research has reported that diets high in monounsaturated fat improve insulin sensitivity in both healthy people and people with diabetes.14 A diet low in saturated fat, but which allows both fish and monounsaturated fat makes sense for people with IRS, because such a diet is associated with protection from heart disease. Recently, a low-fat diet allowing fish was shown to decrease insulin resistance in people with IRS.15
High-carbohydrate diets have also been shown to improve insulin sensitivity; the reason for this may partly be that weight loss often occurs on this type of diet,16 or that these diets are low in fats, such as saturated fat, that worsen insulin sensitivity.17 18 The type of carbohydrate consumed may influence the effect of a high-carbohydrate diet on insulin sensitivity. Animal research suggests that very high intake of fructose or sucrose worsens insulin sensitivity, but human studies have been inconsistent.19 20 “Glycemic index” refers to the blood sugar-raising effect of a food, and there is preliminary evidence from some,21 22 23 though not all,24 human research, that consumption of low glycemic index foods improves insulin sensitivity. Effects on glycemic index may be one reason dietary fiber is associated with better insulin sensitivity.25 As with dietary fat intake, it makes sense for people with IRS to choose carbohydrates according to their effects on heart disease risk. Therefore a diet low in refined carbohydrates and high in fiber appears most prudent.26
Very little research has investigated the effect of increasing dietary protein intake on insulin resistance in people with or without IRS. One controlled study found that people with some features of IRS lost more weight on a high protein diet than on a high-carbohydrate diet, although both diets produced similar improvements in a measurement of insulin sensitivity.27 Preliminary and controlled trials in people without IRS have also shown that substituting protein for carbohydrate in a low-fat diet can improve blood lipids (cholesterol, triglycerides and HDL) towards reduced heart disease risk.28 29 More research is needed on the effects of high protein diets in people with IRS.
In two controlled studies,30 31 a combined program of a weight-loss diet lower in fat and higher in fish, along with exercise three times per week, improved several measures of insulin resistance, blood triglycerides and cholesterol, and blood pressure in a group of people with IRS.
High salt intake decreases insulin sensitivity in young, healthy people,32 but not in older people with hypertension,33 according to preliminary studies. Moderate restriction of salt, however, also decreased insulin sensitivity in one preliminary study of healthy people,34 but had no effect in other studies of people either with35 36 37 or without38 39 hypertension. No studies have investigated the effect of salt intake or restriction in people with IRS.
Lifestyle changes that may be helpful for insulin resistance syndrome
Obesity, especially when fat accumulates in the abdominal region, increases the severity of insulin resistance,40 41 and has been associated with IRS.42 43 Loss of excess weight tends to improve insulin sensitivity (i.e., reduce insulin resistance),44 45 and this has been recently shown to be true for people with IRS as well.46 Weight loss also reduces many of the other health risk factors associated with IRS.47
Cigarette smoking, in most,48 49 though not all,50 studies, as well as exposure to secondhand smoke51 and use of nicotine replacement products,52 53 have been associated with insulin resistance. While smoking cessation has been shown to increase insulin sensitivity in healthy people,54 no research has investigated the effect of quitting smoking on people with IRS.
Alcohol consumption in the light to moderate range is associated with better insulin sensitivity in healthy, nondiabetic people.55 56 57 58 Since alcohol consumption also reduces other risk factors for heart disease,59 60 it does not appear that people with IRS would benefit from avoiding alcohol if they are currently light to moderate drinkers. However, alcohol is potentially addicting and can increase the risk of other diseases, so people with IRS who are not users of alcohol should consult a doctor before starting regular consumption of alcoholic beverages.
Either aerobic exercise or strength training improves insulin sensitivity in both healthy and insulin-resistant people in most studies, 61 62 though a recent controlled trial found that aerobic exercise alone did not affect insulin resistance in people with IRS.63 Studies comparing strength training to aerobic exercise in insulin-resistant people have reported greater benefits from strength training,64 65 but a combination of the two will probably be more effective than either one alone.66 67 In addition, exercise has many benefits in reducing many of the risk factors associated with IRS.68
Some popular diet books claim that insulin resistance causes weight gain and prevents successful weight loss. However, one controlled study found no difference in the number of women experiencing successful short-term weight loss between women with or without insulin resistance.69
Insulin sensitivity decreases after certain stressful experiences, such as surgery,70 and decreased insulin sensitivity is associated with work-related mental and emotional stress,71 and other aspects of a stressful lifestyle.72 However, these associations have not been explored in people with IRS, nor has stress reduction been investigated as a treatment for IRS.
Nutritional supplements that may be helpful for insulin resistance syndrome
Glucomannan, a type of water-soluble dietary fiber, may reduce many risk factors in people with IRS. A double-blind trial found that 8–13 grams per day of glucomannan significantly improved several measures of blood cholesterol control and one measure of blood glucose control in people with IRS.73 Another double-blind study of healthy people found that 30 grams per day of guar gum, a fiber similar to glucomannan, improved insulin sensitivity and many other components of IRS, including blood pressure and blood glucose, cholesterol, and triglycerides, leading the authors to recommend guar gum for people with IRS.74 However, in another study, obese people taking 8–16 grams per day of guar gum for 6–12 weeks did not experience any change in insulin sensitivity.75
Vitamin E, 800–1,350 IU per day, has been shown to increase insulin sensitivity in both healthy76 and hypertensive77 people in double-blind studies. Research is needed to investigate this effect in people with IRS.
One double blind trial found that 1,500 mg per day of calcium improved insulin sensitivity in people with hypertension.78 No research on the effects of calcium in people with IRS has been done.
Magnesium deficiency can reduce insulin sensitivity,79 and low dietary intake80 and low blood levels81 of magnesium have been associated with greater insulin resistance in nondiabetic people. However, no studies of magnesium supplementation in people with IRS have been done.
Chromium has long been known to be helpful to people with insulin-related disorders.82 83 While no chromium research has been done specifically on people with IRS, known mechanisms of chromium’s effects indicate that chromium plays a role in promoting insulin sensitivity.84 85 Preliminary evidence also suggests that insulin resistance may cause loss of chromium from the body, increasing the likelihood of chromium deficiency.86
Preliminary studies have reported that low zinc intake is associated with several of the risk factors common in IRS,87 and a low blood level of zinc is associated with insulin resistance in overweight people.88 However, people with IRS have not specifically been studied to determine whether they are zinc deficient or whether zinc supplements are helpful for them.
A double-blind trial showed that coenzyme Q10, 120 mg per day, reduced glucose and insulin blood levels in people with high blood pressure and heart disease.89 These results suggest that coenzyme Q10 may improve insulin sensitivity in people with components of IRS, but more research is needed.
Are there any side effects or interactions with insulin resistance syndrome?
Refer to the individual supplement for information about any side effects or interactions