TL:DR – Just Tell Me The Facts
This is a long in depth blog post and really takes a deep dive down the nerd chute. It dives down deep on a study comparing an animal-based low carb diet and a plant-based low fat diet. If you just want a summary of what the study found here you go.
- People on the animal-based diet lost more weight but a majority of that weight was water weight. Participants on the plant-based diet lost more fat mass.
- Both diets caused participants to consume less calories, but the plant-based diet caused participants to consume 550-700 calories less than the animal-based diet.
- Both diets caused participants to feel satiated.
- Based on the data collected from the CGMs researchers, found that average glucose over the two week period was higher for the plant-based diet which averaged 94.3 mg/dl versus the animal-based diet which averaged 81.3 mg/dl.
- Glucose tolerance was worse after 2 weeks on the animal-based diet compared to the plant-based diet. Mean glucose during the glucose tolerance test for the plant-based diet was 115 mg/dl while mean glucose during the animal-based diet was 143 mg/dl.
- Fasting blood sugar and insulin improved on both diets. Participants on the animal-based diet experience a significant lowering of C-Peptide indicating a reduction in insulin secretion.
- Triglycerides decreased on the animal-based diet while they increased on the plant-based diet.
- Total cholesterol decreased on both diets but only significantly for the plant-based diet. LDL cholesterol lowered on the plant-based diet but increased on the animal-based diet.
- HDL cholesterol decreased on both diets, but more on the plant-based diet. The bigger increase in triglycerides and bigger decrease in HDL on the plant-based diet resulted in a worse triglyceride to HDL ratio on the plant-based diet
- The animal-based diet experiences a shift in LDL particle size to include more small dense LDL cholesterol.
If you want to know which diet is better click here to read my conclusion after reading the study.
If you want the nitty gritty details, read on!
There is no hotter debate in the nutrition space right now than whether plant-based or animal-based diets are better for you and the planet. In this blog post I will review a recent study that tries to provide an answer to the impact of the different diets on your health. The question of which diet is best for the planet is one I am not qualified to answer 😀.
Before we dive into the details of the study, I will tell you upfront that I have never tried a plant-based diet, I have consumed an animal-based diet for my entire life, and have done extensive experimentation with a low carb version of that diet. I am sure that injects some bias into this blog post, however I tried to look at the evidence objectively and give credit where credit is due to the plant-based diet, as well as look for explanations as to some oddities in the data. I am not against plant-based diets, clearly these diets work very well for some individuals, I just personally prefer an animal-based diet.
The study we will be looking at in this blog post as the basis for our comparison is entitled
A plant-based, low-fat diet decreases ad libitum energy intake compared to an animal-based, ketogenic diet: An inpatient randomized controlled trial [1].
The study had a 2 week cross over design, participants spent 14 days on the plant-based low fat diet and then switched and spent 14 days on the animal-based high fat diet. The plant-based diet had a macro breakdown of 389 grams of carbohydrates, 24 grams of fat, and 72.5 grams protein while consuming 2064 calories. The animal-based diet had a macro breakdown of 67 grams of carbohydrates, 228 grams of fat, and 106 grams of protein, while consuming 2753 calories.
The nice part about this study was that participants were admitted to the NIH Clinical Center and were presented with all meals and snacks. This means unlike most diet studies, this study did not rely on food recall questionnaires, which can be notoriously inaccurate. Participants were presented with 3 meals a day, they had an hour to consume the meal and then the meal was taken away and researchers calculated how much each participant consumed. Participants also had access to snacks and could consume however much they wanted.
Meals were very much whole foods based. The plant-based diet did contain food items that some would consider processed foods like bagels, bread, pasta, and in one meal pretzels. Snacks were dried fruit. The animal-based diet did contain more vegetables than I thought they would include but was also very heavy in high fat dairy products like cheeses and creams etc. Snacks were different types of nuts.
Overall I think the food the researchers presented were pretty accurate for what the average person would eat on both diets.
Researchers tracked weight, body fat, as well as a variety of the blood markers over the course of the 4 week study.
Weight Loss, Fat Mass, and Lean Mass
When it came to weight loss participants on the plant-based diet lost 1.09 kg, while participants on the animal-based diet lost 1.77 kg. While the animal-based diet lost more weight, it was not statistically significant. In addition when we look at what exactly was lost on the animal-based diet it appears on the surface that most of the weight loss on the animal-based diet was from lean mass, in other words they lost muscle. The plant-based diet resulted in significant fat mass loss after the first and second week while the animal-based diet did not.
While this looks like a bad thing for the animal-based diet, it may not actually be as bad as it appears. One thing we know happens when people start a low carbohydrate diet is that they lose a lot of water weight due to the depletion of glycogen in the body [2]. We also know that water shows up as lean mass on DEXA scans [3]. My thought is that much of the fat free mass loss on the animal-based diet is due to water loss and not actually muscle loss. The study authors do point out that fluid shifts will cause changes in fat free mass via DEXA but would not affect fat-mass changes in the scan.
Ultimately my take away from this is that the plant-based diet appeared to lose more fat-mass than the animal-based diet. At the same time just because it appears the animal-based diet may have lost muscle mass that is most likely not the case, rather it was just loss of water weight due to glycogen depletion.
Caloric Intake
Another interesting difference when it came to comparing the two diets was the amount of calories participants consumed when on the diet. The plant-based diet participants spontaneously consumed 550-700 calories per day less than the animal-based diet. The difference in caloric intake is not surprising as consuming a large amount of plant-based foods will fill you up quickly without providing you with a large amount of calories.
In the long term this can make a difference on weight loss. In the course of the two week study this difference in caloric intake did not make a difference when it came to weight loss, but could be beneficial over the long term in a real world situation.
Fullness
Another important factor when it comes to fat loss and caloric intake is how satisfied you feel. You can only take that feeling of being hungry for a short period of time before giving in and eating more. A good sign for both diets is that participants reported feeling satisfied on both diets, in other words, they did not feel hungry even though they were consuming a lower amount of calories.
Blood Glucose
The next interesting data pointed tracked in this study revolved around glucose. Researchers had participants outfitted with continuous glucose monitors (CGM) throughout the study, in addition they provided a liquid meal test at the end of the second week of each study to measure metabolic responses to the meal, and finally they also performed an oral glucose tolerance test.
Based on the data collected from the CGMs researchers, found that average glucose over the two week period was higher for the plant-based diet which averaged 94.3 mg/dl versus the animal-based diet which averaged 81.3 mg/dl.
When researchers looked at glucose over the course of 2 hours after a meal they saw higher readings from the plant-based meal (102 mg/d)l than the animal-based meal (80.5 mg/dl).
Looking specifically at the liquid meal tests, the plant-based diet also resulted in higher glucose readings after two hours than the animal-based diet.
Unsurprisingly, the animal-based diet resulted in higher free fatty acids and triglycerides.
At the end of the 2 week diet period a glucose tolerance test was performed. The animal-based diet resulted in worse glucose tolerance than the plant-based diet. Mean glucose during the test for the plant-based diet was 115 mg/dl while mean glucose during the animal-based diet was 143 mg/dl.
Insulin during the glucose tolerance test was not significantly different.
I find the metabolic information gained from this study to probably be the most interesting and impactful piece of data. There are quite a few key takeaways from this data.
We can clearly see that if you eat an animal-based low carb diet your glucose is going to be very low. To have averaged 81 mg/dl over the course of 2 weeks is pretty impressive. To barely even crack 90 mg/dl two hours after a meal is also very good. We can also see if you are on an animal-based low carb diet, that consuming 75g of carbs at one time (as is done during an oral glucose tolerance test) is probably a bad idea. Ideally you want to keep your glucose below 140 mg/dl at all times and certainly don’t want it going above 160 mg/dl. You can see the animal-based low carb diet peaked at just over 170 mg/dl during the oral glucose tolerance test, no good! This glucose intolerance is likely just temporary. A few weeks of consuming a moderate amount of carbs after being on a low carb diet would likely restore glucose tolerance to normal levels [4].
The plant-based high carb diet did have a higher average glucose over the 2 week trial, but 94 mg/dl is not all that bad considering they were consuming close to 400g of carbs a day. The spike after the liquid meal test was below 120 mg/dl and the area under the curve is small. You could argue that the big jump from 88 mg/dl to 120 mg/dl is quite a big delta, but it’s not unusual when consuming liquid carbs either. The plant-based participants also fared much better on the oral glucose tolerance test as well, with a peak around 130-140 mg/dl. The one thing that I would like to see is what their blood sugar control would look like over a longer period of time. Our bodies are quite good at handling acute stressors like two weeks consuming 400 grams of carbs, but the long term stress of taking in that amount of carbs can result in less favorable blood sugar control over the long run.
Fasting Blood Markers
Outside of blood sugar control researchers also looked at various other blood markers to see if there were any significant changes over the two weeks. Fasting glucose and insulin both decreased significantly over the course of the two weeks on the animal-based and plant-based diets, however there was not a significant difference between the two diets. Baseline glucose was 91 mg/dl, that lowered to 84 mg/dl on the animal-based diet and 85 mg/dl on the plant-based diet. Baseline insulin dropped from 11.3 to 7.4 on the animal-based diet and 8.3 on the plant-based diet. Those are some fantastic improvements in just two weeks!
Interestingly C-Peptide on the animal-based diet was significantly lower from baseline and the plant-based diet. Baseline C-Peptide was 2.18 ng/ml, that lowered to 1.57 ng/ml on the animal-based diet and 1.93 ng/ml on the plant-based diet. This shows a lowering of insulin secretion on the animal-based diet. That does not mean the plant-based diet reading was out of range though, or anything to be concerned about.
Another interesting difference between the two diets was triglycerides. Baseline triglycerides were 75.5 mg/dl. On the animal-based diet that lowered to 63.4 mg/dl but on the plant-based diet they went up to 93.3 mg/dl. Anywhere between 50-100 mg/dl is optimal, so the increase close to 100 mg/dl in just two weeks on the plant-based diet is a concerning trend.
Total and LDL cholesterol decreased significantly on the plant-based diet from baseline and from the animal-based diet. Baseline total cholesterol was 162 mg/dl and baseline LDL cholesterol was 87.9 mg/dl. Total cholesterol dropped to 161 mg/dl on the animal-based diet and 120 mg/dl on the plant-based diet. LDL cholesterol went up to 92 mg/dl on the animal-based diet and went down to 65 mg/dl on the plant-based diet.
There is too much nuance around what constitutes good or bad cholesterol numbers to understand the implications of these changes. Total cholesterol is still well within a “normal range” (and that range is debatable) on both diets.
Does total and LDL cholesterol being lower on the plant-based diet make it better?
Does the increase in LDL on the animal-based diet make it worse?
Hard to say.
If cholesterol numbers continue to increase over time on the animal-based diet it could be a concern. However from the two week experiment there is nothing to be too concerned about.
Another slightly concerning trend in cholesterol on the animal-based diet was the shift in LDL particle size. Small dense LDL particles are considered problematic as they are the ones that tent to get stuck in the artery walls [5]. Large “fluffy” LDL is generally considered fine as they are too big to get stuck and accumulate.
On the animal-based diet the small dense LDL particles increased significantly from baseline while the large fluffy LDL decreased significantly. The plant-based diet saw a significant decrease in the small dense LDL and a non-significant decrease in large fluffy LDL. Again we would need to see what this trend looked like over the long term, but it is something to be aware of.
HDL decreased on both the plant-based and animal-based diet going from a baseline of 54 mg/dl to 47 mg/dl on the animal-based diet and 37 mg/dl on the plant-based diet. In general, we always want our HDL to increase, so the decrease is not a good thing for either diet. It is especially concerning for the plant-based diet.
Why?
Because one’s triglyceride to HDL ratio is a good marker of heart disease [6].
If we calculate the triglyceride to HDL ratio for the animal-based diet it comes out to 1.3. On the plant-based diet the ratio is 2.5. Ideally we want this ratio to be 1 or below. This is why the raising of triglycerides and lowering of HDL on the plant-based diet is a bit concerning.
Another important marker where we see a significant difference is hsCRP, a marker of inflammation. Optimally we want this marker to be 0-0.5 mg/L. Baseline was 2.1 mg/L and that stayed the same for the animal-based diet but lowered to 1.2 on the plant-based diet. It is certainly a good sign the plant-based diet decreased hsCRP but we cannot say that the animal-based diet was the reason that hsCRP did not decrease. hsCRP is affected by too many other factors to say diet alone is the sole reason.
Who Is The Victor?
If you have made it to the end of this blog post, I congratulate you, you are just as nerdy as me 🤣.
The ultimate question we need to answer about this study is does it give us any evidence for which diet is better, animal-based low carb or plant-based low fat?
In my opinion it does not.
The number one reason why we can’t come to any conclusion about which diet is better is the time period over which the research was done. Clearly two weeks eating a diet can make a difference in certain health markers, but it is not nearly enough time to say conclusively how a diet may affect any one individual. We know for both diets, animal-based or plant-based, that people often only show detrimental effects after years of following these diets.
In addition every person is going to have an individual response to a certain way of eating. A diet rich in plants might be completely fine for someone while at the same time being a nightmare for another. Individuality in diet selection is always going to take precedence over any kind of study, no matter how well done it is.
I also end up asking myself, what about an animal-based moderate carb diet? Or a plant-based diet that is moderate fat and moderate carb? Why do we need to be on the extreme end of the spectrum?
This brings me to where I often land when it comes to diets…I don’t think most people need extremes. Most people probably will do fine eating plants, animals, healthy fats, and whole food carbs. If you are metabolically unhealthy, lowering your carbs for a period of time will certainly help, but that does not mean you can never eat a banana again. Similarly if you have a ton of GI issues eating a carnivore diet may give you gut time to heal enough so you can tolerate plants again. A lot of people see their cholesterol skyrocket eating a high fat diet, but when they eat a more low fat plant-based diet their cholesterol comes right back in line. Does that mean they can’t eat animal products or never eat high fat yogurt again? No.
In addition, an animal-based and plant-based diet have one important thing in common with each other. They bring us closer to our ancestral norm. They eliminate processed, hyper-palatable foods.
A few tweaks in one direction or the other, more of less animal products, more of less fat, more of less carbs to fit what works best for you is a very small difference. You are still eating REAL FOOD and that is what is important! Correcting ancestral mismatches like we find in our diets and teaching you exactly how to do that, is the goal of all the content I put out. If you want to learn more about how to correct ancestral mismatches to help you achieve your own goals, use the form below to sign up for my newsletter and get actionable information you can put to use to help you get there.
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