Tuesday, November 13, 2018

Can your genes predict the best weight loss diet for you?

The Study
It has been hypothesized that your genetic makeup can predict which weight loss strategy will be the most effective for you. In this interesting study, 609 adults were randomized to either a low-fat or low-carb diet for 12 months. Previous research has suggested that a certain genotype that impacts carbohydrate metabolism may help a person be more successful with a low-carb diet. Similarly, another genotype that influences fat metabolism has been identified that may make a person more successful on a low-fat diet. Before the trial began, subjects were tested for this low-fat or low-carb response gene sequence.  

Among the participants randomized to the low-fat diet, 130 had the low-fat gene and 83 had the low-carb gene. Among the participants randomized to the low-carb diet, 114 had the low-fat gene and 97 had the low-carb gene. By the end of the 12 month follow-up, there were no differences in weight lost between the two groups and neither the low-fat or low-carb genotype predicted weight loss success.
Journal of the American Medical Association 2018; 319:667.

Take Home Message
Although the idea that our genes can tell us what weight loss diet is best for us is intriguing, this study does not provide evidence that this is the case. More research is needed before we can definitively answer this question.

Dietary Insulin And Colon Cancer

The Study
In this investigation, Harvard researchers created a dietary scoring system of foods that promote a high insulin response. They called it the Empirical Dietary Index for Hyperinsulinemia (EDIH). This is different than the glycemic index, which focuses on the blood sugar effects of carbohydrate containing foods. This index includes all foods that spike insulin after consumption. 

The food groups that contributed to a high EDIH score include red meat, low energy soda, cream soups, processed meats, margarine, poultry, French fries, fish, sugar sweetened beverages, tomatoes, low fat dairy and eggs.

The food groups that contributed to a low EDIH score included wine, coffee, fruit, high fat dairy products and green leafy vegetables.

Over 120,000 men and women from the Nurses’ Health Study and the Health Professional Follow-up Study had an EDIH score calculated for their diet and were followed for 26 years. Subjects with the greatest EDIH score had a statistically significant 26% higher risk of colon cancer when compared to subjects with the lowest EDIH score. American Journal of Clinical Nutrition 2018; 108:363-70.

Take Home Message
When choosing a diet to promote weight loss, you always want to look at the long-term health effects of the diet as well.   

The EDIH score takes the idea of the glycemic index a step further. The GI focuses on the blood sugar effects of carbohydrate foods. The EDIH score includes any food that increases insulin. A lot of these foods are proteins. Many popular current diets are really high in animal protein, and this study makes you think twice about them. 

As far as mechanisms go, it is thought that very high levels of insulin, and insulin derived growth hormone may be carcinogenic. 

In addition to keeping your glycemic index low, it is a good idea to go easy on the animal proteins. It is particularly important to limit red meat and processed meats. It is also a good idea to substitute vegetable proteins such as beans, nuts, whole grains and legumes for animal proteins whenever possible.

Carbohydrate Consumption And Mortality

Carbohydrate consumption has been a hot button issue in the field of nutrition for decades. The type and amount of carbohydrate we should be including in our diets is the subject of intense debate in both the research and weight loss communities. This is a subject that is near and dear to my own heart since carbohydrate metabolism was the subject of my own doctoral research. A new study has been published on this topic that is well done and very important.

The Article
This investigation actually consists of two separate studies (Reference 1). The first is a prospective cohort study using the ARIC cohort (The Atherosclerosis Risk in Communities). The second is a meta-analysis including 7 separate studies.

Prospective Cohort Study in the ARIC Cohort
Over 15,000 adults aged 45-64 years in 4 U.S. communities had their diet assessed by means of a food frequency questionnaire and were followed for 25 years. Subjects who consumed 50-55% of their calories as carbohydrate had the lowest mortality rate. Subjects who ate more or less carbohydrate had an increased mortality risk.

-A 50 year old subject consuming less than 30% of calories as carbohydrate would have a projected life expectancy of 29.1 years.

- A 50 year old subject consuming 50-55% of calories as carbohydrate would have a projected life expectancy of 33.1 years.

A 50 year old subject consuming greater than 65% of calories as carbohydrate would have a projected life expectancy of 32 years.

The meta-analysis consisted of 8 separate studies with a total of 432,179 subjects and showed a similar result. There was an increased risk of mortality with both a low and high carbohydrate intake when compared to a moderate carbohydrate intake.

Subjects consuming less than 40% of calories as carbohydrate had a statistically significant 20% higher risk of mortality.

Subjects consuming greater than 70% of calories as carbohydrate had a statistically significant 23% higher risk of mortality.

Substituting animal fat and protein for carbohydrate resulted in an increased risk of mortality.

Substituting vegetable fat and protein for carbohydrate resulted in a decreased risk of mortality.

Conclusions And Recommendations
Many people manipulate their carbohydrate consumption in an effort to lose weight. It is really important to examine what effect these weight loss diets may have on long term health. My professional goal has always been to provide a strategy that helps my client lose weight effectively, while improving overall health and decreasing risk of chronic disease. 

This study sheds some light on the long-term health effects of diets that severely manipulate carbohydrate consumption. The mechanisms are pretty straight forward. A low carb diet will generally include less healthy foods such as fruits, vegetables and whole grains and higher amounts of red meat and saturated fat. This results in fewer vitamins, minerals, fiber and cancer fighting phytochemicals. This eating pattern likely results in higher levels of oxidative stress, inflammation and biological aging.

On the other hand, diets very high in carbohydrates tend to include too many refined carbohydrates and not enough healthy vegetable fat. This results in a much higher dietary glycemic load, which has been associated with many negative health outcomes.

Here is what we learn from this important study:
1) Going very low carb is probably not a great idea.

2) Going very high carb is probably not a great idea.

3) Stay in the mid carb range, which is around 50-55% of calories.

4) The quality of carbohydrates consumed is of the utmost importance. Focus on low glycemic carbs such as fruits, vegetables, legumes and whole grains.

5) The majority of your fat should be vegetable fats such as nuts, avocado, nut butters, seeds and healthy vegetable oils such as olive oil and canola oil.

6) Minimize sources of protein that are high in saturated fat, especially red meat and processed meats like bacon, sausage, pepperoni, hot dogs, etc. 

1) Seidelmann SB, et al. Dietary carbohydrate intake and mortality; a prospective cohort study and meta-analysis. Lancet Public Health 2018; 9:pe419-e428.