Plant-based versus Ketogenic diets: What is the evidence?

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The field of nutrition is filled with population-based studies. Part of that is because it’s incredibly difficult to do a randomized controlled study and to do it long enough to get meaningful results.  Thus, the debate over which is the better diet is endless. Is it a low-carbohydrate or a low-fat diet? Let’s take a look at a well-designed, randomized, controlled trial looking to answer the question of what works better for weight loss: A Whole Foods plant-based diet rich in carbohydrates and low in fat or an animal-based ketogenic diet low in carbohydrates and high in fat.

Ketogenic Diet

Before jumping into the research, it’s essential to define a ketogenic and plant-based diet. There are so many variable definitions, so we want to be on the same page. When you talk about a classic ketogenic diet, that’s the one with a 4:1. That’s another way of saying that the fat content is four times compared to the protein plus carbohydrate content. So it’s 80% fat and 20% carbohydrates plus protein.

Another variation of the ketogenic diet is a modified Atkins diet.  It follows a 1:1 ratio of fat to protein plus carbohydrates.  By allowing for more protein and carbohydrates, it’s more tolerable for some. 

The 3rd variant is the Low glycemic index treatment (LGIT).  LGIT allows for more carbohydrates, roughly 40 to 60 grams per day. However, all the carbohydrates must have a low glycemic index. The fat content is here is lower at about 60% versus 80% plus percent in the classic ketogenic diet.

Finally, you have the supplements such as medium-chain triglycerides (MCT) or ketone esters. These supplements may help in getting to ketosis faster.

Plant-based diet

When people talk about plant-based diets, they often think of vegetarian diets.  There are lots of vegetarian diet varieties, and it’s important to know the differences.

The first variation is the flexitarian diet. This allows for eggs, dairy, and a little meat, poultry, and fish.

Next is the pescatarian diet. This allows for fish but no meat or poultry.

Then there is the vegetarian diet. Here we have eggs (ovo), dairy (lacto) but no meat, poultry, or fish.

Lastly, we have a vegan diet. This is the strictest with no animal foods.

At SELF Principle, my definition of a plant-based diet is: minimally processed fruits, vegetables, whole grains, legumes, nuts,  seeds, herbs, and spices. There are no animal products, including red meat, poultry, fish, eggs, and dairy products.


Now, let’s get into the research. Here is a randomized control study in which the authors looked at the effects of a low-fat, minimally processed, plant-based diet against low carbohydrate, high fat ketogenic diet.

The authors told the participants that they were allowed to eat as much as they wanted (ad libitum) and that study was not measuring weight loss study. The authors wanted to assess the two classic models of weight gain.

Carbohydrate-Insulin Model

The first one is the carbohydrate-insulin model. The concept is that high carbohydrate diets will lead to an excess in insulin secretion, more calorie deposition in fat stores, increased hunger, and less energy expenditure. Thus, eating a carbohydrate-rich diet will lead to overall weight gain.

Passive overconsumption of energy Model

In the passive overconsumption mode, eating high-fat foods leads to weight gain. The theory is that high-fat foods are energy-dense and dietary fats have a weaker effect on satiety or your sense of fullness.

Let’s see how the results of this study support or refute these two models.

Study Design

This was an inpatient crossover study with 20 healthy, non-diabetic adults. All the participants got exposed to both arms. The first arm was an animal-based, low carbohydrate ketogenic diet with 10% carbohydrates and 75% fat. The second arm was the plant-based low-fat diet, with 75% carbohydrates and 10 percent fat. Both arms were low in ultra-processed foods and matched for nonstarchy vegetables.

All the participants had daily weights and vital signs.  They wore accelerometers and continuous glucose monitors throughout the study. And finally, one day per week, they had them sit in a respiratory chamber to measure their energy expenditure to track their diet’s impact on calorie burn.


All right. So let’s start with the results. What did they find?

Starting with energy intake, the authors found that the folks in the low-fat plant-based diet arm consumed close to almost 700 calories less than the low carb diet arm. This difference remained consistent over the two weeks. Moreover, the authors found no significant differences in hunger, satisfaction, fullness or eating capacity with both the plant-based and ketogenic diet group.  Remember, one of the critical things that derail people’s diet is hunger.

Weight Loss

Now, what about weight loss? The ketogenic group had more weight loss than the plant-based diet group: 1.8 kg versus 1.1 kg.  What’s interesting was the type of weight loss the two groups had.  The ketogenic group had more fat-free weight loss, such as muscle or water.  The plant-based diet group had more fat loss.  Thus, plant-based diets did not only have a calorie reduction, their hunger didn’t change, and they also reduced fat mass.

Sugar levels after a meal

When the researchers looked at postprandial glucose levels, they were much higher in the plant-based diet arm than the ketogenic diet. The question is, what is the impact of this finding? The study was only two weeks, so it’s hard to tell.

The story doesn’t end there. When the authors looked at glucose and insulin levels after an oral glucose challenge, the results were even more surprising. The glucose levels shot up much higher in the ketogenic arm than the plant-based arm.  However, the insulin secretion was the same in both arms.  Thus, insulin resistance was developing in the ketogenic diet in just two weeks of following a ketogenic diet.

Bottom Line

So what is the bottom line that you can take from this study? First, we mentioned two models of obesity, the carbohydrate-insulin model and the passive overconsumption of energy model. 

Looking at the data, the carbohydrate-insulin model did not hold true. The folk in the plant-based diet lost weight on a high carbohydrate diet. Similarly, the participants in the ketogenic diet lost weight on a high-fat diet.

Okay, so both diets had weight loss, but which one should you follow? Based on this research, the plant-based diet allowed participants to cut down calories, lose more fat mass, and did not increase their hunger.  Also, I have reviewed a plethora of studies looking at plant-based diet benefits on brain health, Alzheimer’s, dementia, depression, cardiovascular health, heart attacks, strokes, GI health, kidney disease, and a myriad of cancers. 

The bottom line here is a Whole Food plant-based diet is great for weight loss, excellent for your health, and the right choice for the environment and our planet’s future.  

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Sean Hashmi MD
Articles: 56

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