The Twins Study

This article was originally published as an op-ed in The Jerusalem Post on Wednesday, 21 Feb. 2024:

There are thousands of good studies that analyze the effect of lifestyle, and especially diet, on our health. These studies run the gambit in terms of types. There are randomized controlled studies, epidemiological studies, laboratory studies, and decades of clinical observations. All the studies reach similar conclusions. Eating a plant-predominant diet, exercising, getting enough sleep, not abusing substances, and controlling our stress has a positive effect.

However, the way these studies on health are set up, there are almost always imperfections. One can always find fault somewhere, no matter what study one looks at.

What happens when we put together a study that eliminates one of the biggest question marks in any study on humans–genetic makeup?  How much do genes play a part in health as opposed to lifestyle behaviors?

Genes and lifestyle

Despite the recent evidence available, there are still many who believe that “it’s all genes.” Dr. Christopher Gardner, nutrition scientist and researcher at Stanford University found a great way to put this to the test.  He set up an experiment where he randomized 22 sets of identical twins into two groups.  Each twin was to either eat a healthy omnivore diet or a healthy vegan diet.  The emphasis here is on the word “healthy.”  No junk food on either diet.

For the first month of the experiment, each person received food delivered to their homes. During the second 4 weeks, they were required to prepare their own food.  Setting up the study this way eliminates the problems of age, gender, and genetic factors.

There were many things that the study’s authors wanted to test.  How would both the omnivores and the vegans fair when looking at:

  • LDL cholesterol,
  • biological aging through measuring the telomeres in the DNA strands,
  • microbiome function,
  • body fat and muscle mass,
  • brain function,
  • fasting insulin levels,
  • and overall weight.

Omnivore diet group

The healthy omnivorous diet group was told to eat enough animal products daily to differentiate from the vegan group. This included (on average) targets of six to eight ounces of meat, fish, or poultry, one egg, and one and a half servings of dairy each day. Aside from animal products, daily targets included three servings of vegetables, two servings of fruit, and six servings of grains or starchy vegetables.

Vegan diet group

The healthy vegan diet group was told to avoid all animal products for the course of the study. Daily targets included six or more servings of vegetables, three servings of fruit, five servings of legumes, nuts, seeds, or vegan meat, and six servings of grains or starchy vegetables.  All study participants were told to choose minimally processed foods, build a balanced plate with vegetables, starch, protein, and healthy fats. They had to choose variety within each food group and individualize these guidelines to meet preferences and needs.


After 8 weeks, the vegan group did better all the way around.  They lost more weight, their LDL cholesterol dropped more, they showed a much healthier microbiome, younger biological aging, and better fasting insulin and triglycerides results.  In some categories, the differences were quite pronounced.

The results of the study were published in JAMA- a very respected medical journal.  The complete results of this study are available online.  If you want the easy way to see it, it has been made into a Netflix

documentary called, You are what your eat. It is worth watching.

Role of genetics

Professor Gardner and his colleagues succeeded in confirming what we already knew, but he did it in a way that put to rest the role of genetics. How much influence do genes have in the overall picture of ischemic heart disease and of chronic disease in general?  Many researchers are putting that number as less than 10%.

One of the things the study examined was the influence of behaviors on epigenetics.  While the DNA of our genes does not change, epigenetics examines what turns various genes on and off. Food has a big part to play.  The bottom line: the more plants that make up the diet and the less meat, poultry, and fish, the better off you are. 

My viewpoint

It’s not a formal study, but day after day, I watch people who are pretty sick turn their various chronic conditions in reverse.  This past week, two of my clients had follow up visits with their cardiologists. Both were able to reduce some of their medications – and they are both only beginning.  One of the cardiologists couldn’t get over the sustained weight loss that the client was having. It’s impressive to see various markers on their blood tests and their blood pressure improving all the time. Best of all is that both clients have reported back to me feeling better and better as the weeks go by.

Same background, different results

Remember, in the twin study, they all came from the same home, the same eating habits and, of course, they are genetically identical.  This study more than any other demonstrates that changing our diet and lifestyle, at any age, will have a pronounced, positive effect on health and longevity. 

Dietary and lifestyle changes are more powerful than any pill that can be swallowed or surgery that can be operated.  The proof is undisputable!  Eating a diet, very low in animal proteins, and processed foods and high in vegetables, fruits, whole grains, legumes with some nuts and seeds will help “add hours to our day, days to your year and years to our life.”


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