Low Carb or Low Fat – Which Diet Works Better?

Dr. Frank Shallenberger, MD

June 14, 2021


If you’re struggling to keep your weight down, what type of diet should you use?

Many doctors I know put their patients on low-fat diets. But the low-carb craze has turned from a fad into a way of life for many people.

Does one work better than the other for taking the weight off? How about the long-term impact? Can you keep the weight off?

Well, two doctors set out to find the answer.

I have talked to you about identical twin studies before. They are a great way to learn about how your genetics influence your health. So they should be a good way to find that perfect diet that everyone is talking about.

What if you took identical twins and put them on two different popular diets? Wouldn’t that help us to learn more about what diet is best?

That’s exactly what these two young doctors recently did. And what happened tells us a lot about fad diets.

The doctors in question are identical twins who both were starting to put on more weight than was healthy. Recently, in an interview with Healthy Living magazine, the twin docs talked about how they decided to do a nutritional experiment on themselves.

In the interview, the doctors admitted that any mention of nutrition in their medical education had “fallen between the cracks.” And they wanted to find out whether it was the fat or the carbohydrates in our diets that were the culprits behind disease and poor health.

The fact that they were identical twins took out the geneti element. So whatever they discovered had to be a result of their diets.

Here’s What They Did

One brother went on an extremely low-fat diet. He ate only the minimal amount of fat to keep him alive.

The other brother went on a high-protein diet that eliminated all forms of carbohydrates, from table sugar to flour to fruit. For the technically minded, his carbohydrate levels were so low that his body started making ketones. Both brothers did this for a month. Here’s what happened.

According to brother number two, both plans were, ultimately, “miserable.” He was the one who chose the low-carb diet. He lost a lot of weight, but he had some nasty side effects. “His breath stank, and he felt constipated. Moreover, he was sluggish and tired, and his brain was in a fog.” When he and his brother raced each other uphill on bikes, he realized that his endurance was shot.

On the other hand, the low-fat brother wasn’t doing much better than his twin. He lost very little weight. And he said that without the fat, everything he ate tasted “like cardboard.” He also had a constant gnawing hunger.

So what can we learn from this not-so-interesting experiment? Exactly nothing. Here’s why.

Not a day goes by that one of my patients doesn’t ask me about a particular diet. It could be the Fuhrman diet, the Paleo diet, the China Study vegan diet, the Pritikin diet, the Atkins diet, acid/alkaline diets, etc. — it doesn’t really matter. Everyone wants to know which one is the best.

It just seems to be in our nature to think that there is a particular diet out there that will keep us healthy. The authors of all these diets insist that their diet is the best. But how can they all be right?

Fact is they can’t all be right. Logic dictates that either only one of them is right or they’re all wrong. So what’s your guess?

Which One Is the Right Diet?

My experience after testing thousands of patients for many years tells me that they are all wrong. Every single one of them. And our twins in this case only bear this out. Two people with identical genetics go on two very different diets and neither one does anything but get worse. And why is that?

The first reason is because the diets were extreme. Extreme diets like the ones I mentioned above work well for only a very few people. Usually they work well only for the person who wrote the book and a few other people. Outside of a very small subgroup of the population, the only thing that will happen from an extreme diet is an extreme imbalance and an extremely unhappy patient. But that’s not all.

Not only is everyone different from the get-go, but we also change over time. So a diet that works well for us when we were young is not going to work for us as we get older. The diet that works for an athlete is not going to work for the weekend warrior. The diet that works for a person with a very physical job is not going to work for a banker. Your lifestyle and environment will determine your best diet even more than your genetics.

The other mistake they made was that they went on the diet for only 30 days. If a way of eating is going to be good for someone, it has to be for the long term. Here’s a general rule of thumb. Never go on any lifestyle improvement program that you know you are not going to commit to for years. None of this stuff works unless you are in it for the long haul.

So How Can You Find the Right Way to Eat for You?

It’s not that hard.

The first issue to tackle is carbohydrates. Why? It’s because excessive carbohydrate is the number one reason why we have so much disease. More than any other single dietary bad habit, it’s responsible for our epidemics of cancer, heart disease, obesity, diabetes, arthritis, and bowel disease, as well as the incredible amount of fatigue, mood disorders, insomnia, and headaches that doctors see every day.

The low-carbohydrate diet that our twin doc used was too extreme. If he had just decreased his carbohydrate intake only to the lowest amount his body needed, things would have been much different. He would have lost the weight, felt great, and shown no ketones. But everyone is so different.

So how could he have known what the right amount of carbs for him would have been? Once again, it’s simple.

I have told you many times before about Bio-Energy Testing. In a perfect world, everyone would have this test every year. It is the single most valuable test you can ever have for your health. One of the reasons for that is that it can tell you if your intake of carbohydrates is excessive or not. It’s not rocket science.

When people eat too much carbohydrate, they decrease their metabolism of fat. Bio-Energy Testing can quantifiably measure fat metabolism. So if it turns out that your fat metabolism is down, then we know that you are eating too many carbs.

How many carbs should you eat? Just the right amount that keeps your fat metabolism in a healthy zone. For some that may mean a high-carb diet. For others, it could mean a very low-carb diet. Bio-Energy Testing can provide the answer without any guess work involved.

It's Not Just Carbs

The second issue to tackle is the nutrient quality of your diet. I have reported to you before that study after study shows that every year the nutrient quality of the average American diet declines. More and more we are eating processed foods that are laced with chemicals and deficient in vitamins, minerals, healthy fats, and amino acids. So don’t be that average American.

Stay away from pre-prepared convenience foods, processed foods, and the restaurants that serve them. Eat fresh, whole foods. Don’t eat foods that come with an ingredients label. That means they are processed and devoid.

Eat plenty of vegetables. Make sure you eat good oils like coconut oil, olive oil, flax oil, and fish oil. And be sure to eat plenty of animal protein like meats, dairy, and eggs.

Should You Become a Vegetarian?

I have tested a fair number of vegetarians and vegans using Bio-Energy Testing and I can tell you that only a handful test out anywhere close to healthy. Sure it works for a few. But it is certainly nothing that should be generally recommended.

And for goodness sake, get a Bio-Energy Test to see where you stand. There is a growing number of practitioners who are offering this test right now. You can find a list of the Bio-Energy Testing Centers at www.bioenergytesting.com. You can also learn more about it, including how it works, at the same website.

Additionally, I discuss it and how to find the right diet for you in detail in my book Bursting With Energy. But whatever way you decide to eat, learn from our twin docs, and stay away from the extreme diets that so many are popularizing.



Weir, Sarah B. “Twin Brothers Put Diet Crazes to Ultimate Test,” Healthy Living, Tuesday, January 28, 2014.

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