Diet and Disease

State of the Art 2017

The hallmark of good healthcare is that it is “evidence-based”.  This simply means that decisions in care and preventative strategies are largely based on quality scientific evidence rather than empirical information.  This is not to say that empirically based knowledge, that based only on practical experience, is not important but that scientifically derived evidence tends to be more accurate in the long run.

Regarding diet, we are emerging from 3 to 4 decades of “this seems to make sense”, rather than evidence-based decision making.  Unfortunately, the common advice has proven quite inaccurate and somewhat contributory to the greatly increasing rates of some chronic diseases such as diabetes.

Given the above state, I thought it was appropriate to celebrate “National Nutrition Month” with a look at the evidence-based knowledge that we have concerning the relationship between diet and disease.  The most striking realization has been that the low fat focus of the past 30-40 years has not only been ineffective in preventing the chronic diseases it was touted to be a solution for, it actually has been contributing to the increased development of most of these very diseases.  There are several reasons for this:

·         Low fat means higher carbohydrate

·         A low fat diet has never been shown to lower blood lipids

·         The low fat/high carb diet causes greater weight gain than comparative diets

·         The low fat/high carb diet causes a greater shift to a disease-causing blood lipid pattern

A little background is necessary to understand this important error that cost Western Nations 30 years of good dietary understanding.  In the 1950’s a physiologist named Ancel Keys reported that in his study of seven western countries, a higher total and saturated fat diet was associated with greater heart disease risk. The problem was that Keys actually studied data from 29 countries but “proved” his theory only reporting that from 7 countries and omitting that from the 22 countries (76%) that found no relationship.  Extensive scientific review has now found this study inaccurate and misleading:

“There is now probably unanimous consensus in the scientific community about this study - it is faked, since Dr. Keys cherry picked just 7 countries. He had data of 22, and when statistical methods are applied - there is no significant relationship between dietary fat consumption and heart disease.”

The reasons why the medical community, which prides itself as being “evidence-based”, dispensed erroneous advice for 3-4 decades are complex.  They are generally looked at as the top source of nutritional advice for disease prevention, yet many studies examining their training and ability to do this suggest otherwise.

A study published in 2006 of over 2300 medical students at 16 representative medical schools found that 72% beginning medical school thought that nutritional counseling was “highly relevant” to medical practice.(1)  By their final year the number had dropped almost in half to 46%.  Only 19% thought that they had been adequately trained to provide this advice, and only 17% reported to doing so with their patients.

A prior study examined the knowledge of internists and cardiologists about the impact of diet on blood lipids.  Eighty-four percent of cardiologists and 96% of internists did not know that a low fat/high carb diet would raise blood triglyceride levels.  Similarly, 70% of cardiologists and 77% of internists did not know that this diet would lower HDL, or good cholesterol.

The problem is that medical education is devoid of nutritional education instead focusing on other areas of concentration.  Nutrition science has not filtered into that training, yet the public perception is that this is where nutritional advice should be available. 

This domain should default to specifically trained individuals well versed in nutritional science, but many barriers to this remain in the system.

The thought process that has led to the standard low fat diet advice for the past 3-4 decades was an oversimplified assumption that the fat responsible for arterial plaque must be generated by dietary fat.  However, the higher carbohydrate dietary pattern that this assumption created actually causes a more risky shift in blood lipid patterns than does a higher fat, lower carbohydrate pattern.

In reality, any energy in excess of immediate need is sent to the liver to be converted to fats as that is the primary energy storage form that humans use.  The sugars from a higher carbohydrate diet have been shown to increase liver triglyceride production, lower HDL production, increase LDL or bad cholesterol production and cause a shift in the LDL particle size to a smaller, more plaque-forming variety.  This combination of changes is the one that causes the greatly increased vascular disease risk in diabetics.

The increase in LDL production associated with a higher carb diet occurs because this diet causes higher insulin levels.  Making cholesterol in the liver requires energy availability, and insulin is a potent signal of energy availability.

Most major bodies that set guidelines about dietary behavior have recently revised their positions stating that the dietary high fat hypothesis has not proven true.  They also suggest that the low fat diet preoccupation has pushed us to a higher carbohydrate diet that has been a potent driver of the obesity and diabetes epidemic. 

Diabetes is of particular concern as vascular complications remain the dominant cause of associated disease and deaths.  Fuel to this concern was added recently by a study that looked at carotid artery plaques in obese and non-obese subjects.  While high dose statin therapy lowers plaque volume by 4.2% in non-obese subjects, obese subjects had it increase 4.8% in 12 months despite lowering of LDL.(3)  Other factors besides LDL contribute to plaque formation including inflammation and glycation, or direct sugar damage to tissue.

The lesson to deduce from the evidence-based look at the current research on diet and disease is that we are generally ill suited to the dietary pattern of the last 30 to 40 years.  While humans thrived on a diet of about 30% protein, 40% fat and 30% complex carbohydrate for the first 6 million years, the current shift to 15% protein, 25% fat and 60% carbohydrate has resulted in growing rates of a number of chronic diseases that have a metabolic basis. The high percentage of total carbohydrate has been further complicated by the dominant amount being refined and with added simple sugars.

So the knowledge base we have concerning diet in 2017 looks very different from the commonly recommended dietary pattern of the last 40 years.  Now we face the difficult task of actually implementing that change, but the motivation is that the stakes are high.

1)    Spencer et al.  PREDICTORS OF NUTRITIONAL COUNSELING BEHAVIORS AND ATTITUDES IN U.S. MEDICAL STUDENTS.  Am J Clin Nutr, 2006;84:655-662.

2)    Flynn et al.  INADEQUATE PHYSICIAN KNOWLEDGE OF THE EFFECTS OF DIET ON BLOOD LIPIDS AND LIPOPROTEINS.  Nutri J, 2003;2:2-4.

3)    Sandfort et al.  OBESITY IS ASSOCIATED WITH PROGRESSION OF ATHEROSCLEROSIS DURING STATIN TREATMENT.  J Am Heart Assoc, 2016;5:e003621.