Low carb diets and heart disease – What are we afraid of?
I find it extraordinary how carbohydrate restriction is repeatedly rejected by the medical community as an alternative approach for obesity, the metabolic syndrome and type 2 diabetes. Obesity has reached epidemic proportions in many countries around the world. Diabetes and other obesity related disorders have become increasingly common. Public health organizations and medical societies usually advocate a low-fat, high-carbohydrate, energy-deficient diet to manage weight. Nonetheless, clinical experience and scientific studies indicate that other approaches may be more effective.
The main argument against carbohydrate-restricted, high-fat diets are concerns regarding their long-term safety. Most such diets encourage increased consumption of animal products and therefore they often contain high amounts of saturated fat and cholesterol. It has been suggested that this may cause unfavorable changes in blood lipids and thereby increase the risk of heart disease. Therefore, several professional organizations have cautioned against the use of low-carbohydrate, high-fat diets.
According to a statement from the American Heart Association AHA, updated january 2012, “eating large amounts of high-fat foods for a sustained period raises the risk of coronary heart disease, diabetes, stroke and several types of cancer”. An older statement from the Heart and Stroke Foundation of Canada claims that ” low carbohydrate diets often lack vitamins and are low in fibre. A low fibre diet can result in constipation and can increase your risk of colon cancer. Low carbohydrate diets tend to replace carbohydrate with fat and protein. High intake of protein can result in large amounts of calcium in the urine, and loss of bone mass. High intake of fat, particularly saturated and trans fat, can lead to atherosclerosis, heart disease or stroke”.
These statements are based on observational data at best. Randomized clinical trials generally don´t support these conclusions. Indeed, low carbohydrate diets have demonstrated their therapeutic value in numerous studies, and often outperform other diets when comparisons are made. Nonetheless, they are still ignored by governments and medical societies. Keep in mind though, that carbohydrate restriction is a matter of definition. Some diabetic associations have accepted moderate carbohydrate restriction as an alternative approach for weight loss in type 2 diabetes.
Doctors, cardiologists included, commonly recommend low-fat, high-carbohydrate diets to patients with heart disease, as well as for cardiovascular prevention. Limitation of saturated fats and cholesterol is advocated. This is what doctors are urged to do by clinical guidelines. The guidelines are written by specially selected experts and published by professional organizations. Interestingly, there is often no mention of individual differences between patients. The low-fat, low saturated fat, low cholesterol, high-carbohydrate approach is recommended for all. It doesn´t matter whether you have high blood pressure, whether you are obese or overweight, have the metabolic syndrome, or whether you have diabetes.
I have nothing against low fat diets. Look at the DASH diet for example. Extensive research indicates that this diet lowers blood pressure and cholesterol, and is associated with lower risk of several diseases, including heart disease. Furthermore, it was recently suggested that the DASH diet may be used for weight loss as well. I would be very satisfied if may patients would stick to the DASH diet. I usually urge them to do so. I am sure it benefits their health. The same thing can be said about a vegetarian diet. I consider such a diet to be a very heart healthy diet. Furthermore, I very often recommend a Mediterranean type diet to my patients. There is a lot of scientific date supporting the use of this diet for cardiovascular prevention as well as for patients with heart disease.
The role of diets takes on a different perspective when it comes to obese patients, and those with the metabolic syndrome, where weight loss is a priority. For years I have struggled with the low-fat, high-carbohydrate, energy-deficient dietary approach to manage these conditions. Simply put, the results have been disappointing. Often weight loss is limited and not sustained, and there are very limited improvements in metabolic function. However, I might admit the lack of result is more often due to lack of compliance than something else. Maybe we provide instructions and recommendations that patients are unable to comply with, no matter how hard they try.
I have found that people suffering from obesity or the metabolic syndrome are much more likely to lose weight and improve their metabolic function on a low-carb, high-fat diet. My clinical experience is that the effects of such a dietary approach on blood lipids is a bit hard to predict. Commonly there is an elevation of total cholesterol and LDL-cholesterol (“bad cholesterol”) which may be considered harmful. However, at the same time there is most often an elevation of HDL-cholesterol (“good cholesterol) and triglycerides are lowered. So the question is; Should I not recommend a dietary approach that works in terms of weight loss and metabolic control, because there may be a slight elevation of LDL-cholesterol? According to the medical associations and the clinical guidelines, I should not.
Low carb diets and heart disease – The scientific studies
My purpose is not to go through all available scientific data on the issue of carbohydrate restriction and heart disease. However, I will try to convince you that the available data does not support the conclusion that low-carbohydrate diets are less safe than other dietary approaches for people who are obese, overweight or suffer from the metabolic syndrome.
The initial recommendations to avoid saturated fat and cholesterol were based on observations from epidemiological research. Some of this research was led by the famous American scientist, Ancel Keys. In a personal reflection from 1995 Keys wrote: “These observations led to our subsequent research in the Seven Countries Study, in which we demonstrated that saturated fat is the major dietary villain.” Keys observed that death rates were related positively to the average percentage of dietary energy from saturated fatty acids, but negatively to dietary energy percentage from monounsaturated fatty acids. In short; saturated fats seemed to increase risk, while monounsaturated fats appeared to lower risk. Since then, an independent association of saturated fats with the risk of heart disease has not been consistently found in epidemiologic studies. Replacing saturated fats with carbohydrates has not been shown to be beneficial. Indeed, replacement of saturated fats with refined carbohydrate can worsen blood lipids when insulin resistance is present, by increasing triglycerides, the number of small LDL particles, and by decreasing HDL-cholesterol. Some studies have indicated that replacing saturated fat with monounsaturated or polyunsaturated fat may be beneficial, although the latter was not supported by the recently published Sidney Diet Heart Study.
The relationship between the consumption of fat, saturated fat in particular was studied in the Swedish Malmö Diet and Cancer Study published in 2007. In this large prospective observational study, no trend towards higher cardiovascular event risk for women or men with higher total or saturated fat intakes, was observed. This study was later included in the much cited Siri-Tariono meta-analysis published 2010, showing no significant evidence for concluding that dietary saturated fat is associated with an increased risk of heart disease.
A number of randomized clinical trials have compared low-carbohydrate diets with other dietary approaches. In many of these studies, low carb diets have resulted in more short-term weigh loss in healthy women, individuals with severe obesity with high prevalence of the metabolic syndrome and type 2 diabetes, overweight adolescents, overweight individuals with hyperlipidemia, and premenopausal women, compared with low-fat diets. Furthermore, negative effects on blood lipids with low-carbohydrate diets were not observed in these studies and markers of the metabolic syndrome were generally improved.
Most of these randomized trials are short term studies. Thus, the long-term effect of low-carbohydrate diets still remains to be clarified. Recently, it has been suggested that such diets may be harmful. In a systematic review and meta-analysis of observational studies, published November last year, Noto and coworkers found that low-carbohydrate diets were associated with a significantly higher risk of all-cause mortality. However, they did not find an association between low-carb diets and the incidence of, and mortality from cardiovascular disease. The authors acknowledge that their analysis is based on limited observational studies, and that large-scale trials on the complex interactions between low-carbohydrate diets and long-term outcomes are needed. It is also necessary to point out that there was a substantial difference between studies, concerning both study design and definitions. Such heterogeneity may make meta-analysis problematic.
Few final words
There are many different versions of low-carbohydrate, high-fat diets. Some promote the consumption of saturated fat, while others don´t. For a patient with heart disease or someone with elevated cholesterol, I usually recommend monounsaturated fat and polyunsaturated fats rich in omega-3. I find that using the Mediterranean approach, when selecting which fats to eat may be very helpful.
Although it does not comply with guidelines, I commonly recommend individuals who are obese or suffer from the metabolic syndrome to cut down on carbohydrates and increase fats. In most instances, I find these recommendations very useful. I don´t recommend my patients to stay in ketosis for long periods of time. However, if they choose to do so, if they feel well, and if their health is improving, I find no reason to tell them not to.
If an obese person with metabolic dysfunction manages to achieve weight loss and improve his or her metabolic function on a low carbohydrate diet, it is hard to understand how such an achievement may be harmful.
I look forward to the day when low-carb, high-fat diets are accepted by public health representatives and medical associations for the treatment of obesity, metabolic syndrome and type 2 diabetes. The medical community, which I am a part of, accepts that drugs that lower cholesterol, and slightly reduce the risk of heart disease (although having considerable side effects, among them increased risk of diabetes) are given to 25 percent of adults in many countries around the world. I find it a bit hard to accept that the same medical community does not accept and recommend a dietary approach for obesity and the metabolic syndrome, that causes weight loss, increases wellbeing and improves metabolic function, and indeed appears to outperform other diets in this respect.