Study Proves Low Fat, Plant-Based Diet is Best For Fat Loss
Key Takeaways
It is difficult and expensive to conduct a well-controlled and meaningful nutrition study.
High levels of insulin and blood sugar fluctuations do not cause weight gain.
Compared to very high fat diets, very high carb diets (75%+), along with low protein and low fat, appear to result in poorer blood sugar regulation.
High carb, low fat diets may be better for weight loss for some people, because the higher volume and lower caloric density of food allows one to feel satisfied while consuming fewer calories.
Human eating is complex. It cannot be explained by a single model.
Full Story
If you’ve been following Solokas Focus for any amount of time, you’ll be suspicious that the title is not entirely accurate. It’s not and, in fact, this headline will never be true. A single study will never “prove” a theory and no one way of eating will ever be “best” for every person. Sensationalization of research is the reason you need to be wary of your information source. It is incredibly easy to, intentionally or unintentionally, misinterpret a study to make it fit your prior bias and support a dogmatic stance on nutrition. This sentiment holds especially true for this polarizing study published just last week (1/21/21), “Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake (1).” I’m going to take an unbiased approach, break down the results, and explain the practical applications.
Not only is my headline inaccurate, but if I chose to interpret this study differently I could have titled this post “Low Carb Diet Superior for Blood Sugar and Insulin Response.” I’m sure that many will cite this study to support a plant based style of eating, while others will use it to support a high fat, primarily animal product diet. The truth is that this specific study does not support either positions and neither headline comes close to conveying the actual results.
This study does not prove that a low fat, plant based is superior for weight loss, or that a carnivore diet is best, but it does illustrate the pros and cons of ultra high fat and ultra high fat carb diets. Ultimately, this intriguing study attempts to answer the age-old question “Is low carb healthier than low fat?” and, in doing so, also assesses the question “Is animal based healthier than plant based?” Let’s dive in.
Study Design
The main points of the study design/participants include:
20 non-diabetic men and women, with an average age of 30 and average BMI of 28
Participants were confined to a metabolic ward (meaning that all food and drink was provided for them) for 4 weeks
It was a crossover design study (i.e. participants consumed the high fat, low carb diet for 2 weeks and then switched to the high carb, low fat diet, or vice-versa)
Participants were told that it was not a weight loss study and that they should eat until satisfied
Low fat diet - 75% carb, 10% fat, 15% protein
Low carb diet - 10% carb, 75% fat, 15% protein
Low fat diet consisted entirely of plant-based products
Low carb diet consisted of 82% of calories from animal products
Both diets were low in ultra processed foods and matched for non-starchy vegetable intake
This was a tightly regulated, well controlled study. Though 4 weeks is a relatively short duration for a diet study, it is a significant amount of time for participants in a metabolic ward (basically a food jail).
Study Results
The highlights of the results include:
“Energy intake during the LF diet was spontaneously reduced by ~550–700 kcal d−1 compared to the LC diet, with participants losing weight and body fat while reporting no significant differences in hunger, fullness, satisfaction or pleasantness of the meals.”
“The LF diet had higher glycemic load and resulted in greater postprandial glucose and insulin levels compared to the LC diet that was higher in energy density.”
“These data suggest that while the LC diet had benefits for reducing glucose and insulin levels, the LF diet had benefits for appetite control.”
Overall, the low fat diet resulted in fewer calories consumed while the low carb diet resulted in better blood sugar management. Now that we know the study design and the primary results, let’s discuss the significance of the findings and my 5 key takeaways.
1. It is tremendously difficult and expensive to conduct a well controlled and meaningful nutrition study.
It is extremely expensive to conduct such a tightly controlled study. In order to conduct the study, researchers paid 20 healthy people to leave their homes and agree to eat only the food that was provided for them for an entire month. Without a doubt, this study is very well designed and controlled (crossover design, metabolic ward, participants were blinded from the conditions) - just about the gold standard of nutrition research.
Despite the strength of the methods, the significance of the results leaves much to be desired. The researchers designed the macronutrient composition of the diet to amplify the potential effects of each diet. Instead of comparing the the effects of a low carb to a low fat diet, they compared an ultra low carb diet to an ultra low fat diet. The authors mention that in previous, similar studies that the fat and carbohydrate levels assigned were not extreme enough to truly be classified as low fat or low carb. As such, they took great measures to ensure that the diets were indeed very low fat and very low carb.
Restricting fat and carbs to only 10% of the calories for the low fat and low carb diets, respectively, limits the practical applications of the study to everyday life. Only a fraction of people would ever adhere to such restrictive diets in an uncontrolled environment, and thus the results lack “real world” applicability. The findings do not translate very well to more balanced diets that are slightly higher carb (i.e. 65% of calories from carbs) or slightly higher fat (i.e. 40% of calories from fat).
This study, though well-designed, expensive, and informative, points to the glaring limitations of nutrition research. It serves as yet another reminder that one study alone will never convey meaningful results and that we must take the entire body of research into account when forming a well informed opinion.
2. High levels of insulin and blood sugar fluctuations do not cause weight gain.
One of the primary goals of the study was to assess the insulin model of obesity, which suggests that higher carb intake leads to higher insulin levels and results in more fat gain compared to lower carb, higher fat diets that do not spike insulin to such a significant degree. As this study showed that the higher carb group had higher blood sugar and insulin levels yet still lost more weight than the high fat group, it certainly disproves this mightily flawed and already debunked theory (2). That being said, just because the high carb diet resulted in a lower calorie intake does not mean it is the superior diet for health and longevity.
3. Very high carb diets (75%+), along with low protein and low fat, appear to result in poorer blood sugar regulation.
The primary concern raised by the results of the high carb, low fat group in this study was the higher variability in blood sugar control and insulin levels. Poor blood sugar control has been shown to be a cause of many adverse health conditions (see the effects of uncontrolled Type 2 Diabetes). Though an unsurprising result, the high blood sugar levels observed in the high carb group present a strong case against an ultra high carb style of eating (note that I wrote ultra high carb, not high carb). As dietary fat has been shown to reduce the post prandial glycemic response, or the extent to which blood sugar levels rise after a meal, it is not unreasonable to speculate that if the amount of fat consumed was higher (i.e. 15-30% rather than 10%) and calories were kept the same that the blood sugar levels would have remained more stable.
4. High carb, low fat diets may be better for weight loss for some people, because the higher volume and lower caloric density of food allows one to feel satisfied while consuming fewer calories.
Though the authors state, that “the determinants of energy intake and body fat change cannot be adequately explained by individual factors such as glycemic load, protein intake, dietary fiber or energy density” it is not unreasonable to speculate that the higher fiber and lower energy density (i.e. same volume of food containing fewer calories) of the high carb diet compared to the high fat diet is a plausible explanation for the lower calorie intake of the high carb diet. In fact, the same lead author, Kevin Hall, came to a similar conclusion in his paper published just last year (4). Moreover, it makes intuitive sense that it would be far easier to overeat while consuming a diet containing primarily calorie-dense foods with 75% of its calories from fat (think eggs, full fat meat and dairy, nuts) than it would be to overeat consuming a low fat, plant-based diet (think huge salads with no added oils, potatoes, and grains).
5. Human eating is COMPLEX. It cannot be explained by a single model.
Finally, the most important takeaway from the study is conveyed by the author’s final line of the paper, “Our results suggest that regulation of energy intake is more complex than these [passive overconsumption model of obesity, carbohydrate–insulin model of obesity] and other simple models propose.” The mistake that many make when trying to figure out the best diet based on individual studies is that human eating behavior is nuanced and cannot be boiled down to one or two variables.
We’re playing checkers when we would be better off playing chess. I don’t blame the researchers, as single studies are informative, thought provoking, and are the bedrock of the scientific process. I do blame the people that manipulate and twist the results of a single study to make it fit their agenda. This behavior only further complicates matters. To attempt to address the obesity crisis by assessing one or two variables, in this case total calories and macronutrient ratios, is liken to playing a game of checkers. Human eating behavior encompasses not only calories and macronutrient ratios, but also food composition, timing, and supplementation, as well as psychosocial and socioeconomic factors.
In actuality, human eating behavior is a chess match. We’re not going to win the chess game by extrapolating from single studies on the level of checkers. Results from studies taken alone will always fail to answer the one question that everyone is trying to figure out, “How should I eat to be the healthiest version of myself?” The only way to resolve this conflict is to consider the body of research as a whole and to integrate the results with one’s personal history, current state, and future goals.
Wrap Up
This new study reinforces the notion that human nutrition is a complex concept that cannot be simplified or categorized into neat, little boxes such as “low fat is healthier!” or “low carb is healthier!” The fact remains that sustainable dietary principles reign supreme over polarizing positions. The answer to “high carb or high fat?” for most people, most of time, almost certainly lies somewhere in the middle. If you’re….
Eating the right amount of calories
Consuming primarily whole, unprocessed foods
Performing the right amount of activity
Prioritizing quality sleep and stress management
In general, focusing on the most important aspects of health and longevity
….then the heated debate of carbs vs. fat will always just be insignificant noise.