No more cholesterol restriction in latest dietary guidelines
Earlier this month, I was forwarded an email by a friend which stated “The truth is finally out – concerns about eating food with high cholesterol is untrue!! Suddenly all of us are gastronomically liberated. We are no longer deprived of our favourite food.”
This email referred to the 572 page Scientific Report of the 2015 Dietary Guidelines Advisory Committee (DGAC) which was submitted to the US government in February 2015 which included a statement, “Previously, the Dietary Guidelines for Americans recommended that cholesterol intake be limited to no more than 300 mg/day. The 2015 DGAC will not bring forward this recommendation because available evidence shows no appreciable relationship between consumption of dietary cholesterol and serum cholesterol, consistent with the conclusions of the AHA/ACC report. Cholesterol is not a nutrient of concern for overconsumption.”
Can we really tuck into our favourite foods and be oblivious of the cholesterol content? The answer to this question requires a review of the 2015 DGAC report and the American Heart Association/ American College of Cardiology(AHA/ACC) Guideline on Lifestyle Management to Reduce Cardiovascular Risk to understand the impact of diet on various aspects of health. The DGAC report looked closely at various diets and especially at the DASH (Dietary Approaches to Stop Hypertension), Mediterranean and the vegetarian diets.
The DASH diet was a US National Institutes of Health sponsored research diet, developed to decrease blood pressure without medication. It is an eating plan that is rich in fibre, protein, potassium and magnesium, comprising plenty of fruits, vegetables, low-fat dairy, nuts, beans and seeds. It is low in sodium, saturated fat, total fat, and cholesterol. The Mediterranean diet is a nutritional plan patterned after traditional diets of Greece, Southern Italy, and Spain.
The main characteristics of this diet include high consumption of olive oil, legumes, whole grains, fruits, vegetables, fish, moderate consumption of dairy products, wine consumption, and low consumption of non-fish meat products. The vegetarian diets included vegan (no meat, fish, eggs, or dairy), lacto-ovo vegetarian (includes eggs and dairy, but no fish or meat), and pesco-vegetarian (includes fish, but no meat) diets.
The evidence from the 2015 DGAC and AHA/ACC guideline on the impact of diet on health are summarised into 2 parts. The first part will summarise the findings on diet and its relationship to heart attacks, stroke, blood pressure, cholesterol and weight loss. Part 2 will summarise the findings on diet and its relationship with diabetes, cancer , birth defects, brain and bone .
Diet and the risk of heart attacks and stroke
Can one really reduce the risk of stroke and heart attack by watching their diet? The good news is that there is strong evidence that this can be achieved by taking a “Healthy Diet” that is characterised by increased consumption of vegetables, fruits, whole grains, low-fat dairy, seafood, and decreased consumption of red and processed meat, refined grains, and sugar-sweetened foods and beverages. Many studies also support the consumption of nuts and legumes.
Nuts in particular are rich in the ”good” polyunsaturated fats and low in the “bad” saturated fats. The net effect of these healthy diets is to lower saturated fat, cholesterol, and sodium and increase intake in fibre, potassium, and unsaturated fats.
Diet to lower blood pressure
Compared to diets that are high in saturated fat and sodium and low in vegetables and fruits, the DASH type diets reduced BP by approximately 6/3 mmHg (upper “systolic” blood pressure/lower “diastolic” blood pressure) . The AHA/ACC guideline also attribute a smaller benefit to Mediterranean type diets. The evidence for vegetarian diet was more mixed with data from randomised controlled trials showing some suggestion that there may be a mild effect in lowering the systolic blood pressure and limited impact on diastolic blood pressure.
Diet and lipids
The DASH diet show favourable effects on “bad” low-density lipoprotein cholesterol (LDL-C) and no effect on triglycerides (TG). Generally, those who converted to a DASH diet showed a LDL-C reduction of less than 10% .There is currently no strong evidence on the impact of a Mediterranean type diet or vegetarian diet on the blood lipids (includes cholesterol and triglycerides)
Diet and cardiovascular disease outcomes
A healthy diet can reduce the incidence of heart attacks, strokes and death. The benefit seen varied from about 20% to more than 50% reduction in risk of heart attacks, strokes and death. This benefit was seen for both the Mediterranean type diet and the DASH diet.
In the largest Mediterranean diet (plus extra virgin olive oil or nuts) trial, PREDIMED, the benefit seen in high-risk subjects when compared to the control group who were advised to reduce fat intake, was so evident that the trial was stopped early. A meta-analysis of seven studies related to heart attacks, stroke and death in vegetarian diet published in the Annals of Nutrition and Metabolism journal in 2012 by investigators from Zhejiang University, found that there was a 9% decrease in overall death, a 29% decrease in deaths from heart artery blockage and a 12% decrease in death from strokes in vegetarians compared to non-vegetarians.
Diet and reduction of body weight
There is strong evidence that obese adults can reduce weight by diets that result in an energy deficit. In the latest National Heart Lung and Blood Institute (USA) Obesity Report, the 12 randomized studies all confirm that for weight reduction, an energy deficit must be achieved by one of the following methods :-
a) a limit of 1,200 to 1,500 kcal/day for women and 1,500 to 1,800 kcal/day for men (adjusted according to body weight),
b) daily net negative energy balance of 500 kcal/day or 750 kcal/day , or
c) consumption of prescribed diet that restricts high-carbohydrate foods, low-fibre foods, or high-fat foods. Overall, maximum weight loss is usually seen at 6 months (4 to 12 kg) and this is followed by a gradual regain in weight over 2 years with a resultant weight loss of about 3 to 4 kg at 2 years.
Despite the popularity of low carbohydrate diets, the 2010 GDAC concluded that “diets with less than 45% of calories as carbohydrates are not more successful for long-term weight loss (12 months). There is also some evidence that they may be less safe. In shorter-term studies, low-calorie and high-protein diets may result in greater weight loss, but these differences are not sustained over time; and a moderate amount of evidence demonstrates that intake of dietary patterns with less than 45% calories from carbohydrate or more than 35% calories from protein are not more effective than other diets for weight loss or weight maintenance, are difficult to maintain over the long term, and may be less safe.”
While the 2015 DGAC does not specify a limit on cholesterol intake, it nevertheless spells out the evidence that the benefits from healthy diet can reduce heart attacks and strokes, 2 of the commonest causes of deaths. Hence, those who have removed all their inhibitions on diet and are waiting to unleash their craving for cholesterol rich foods will be disappointed that these unrestrained food adventures do come with hefty cost to their health.
** This is the first of two parts on diet and health.