Here we go again. Two new studies came out recently that grabbed impressive headlines about what we should or should not eat. Unfortunately, once again the details may not warrant the high publicity. I have warned about the pitfalls of nutritional research before. Nutritional research is hard. Epidemiological studies require food recall, leave too many variables uncontrolled, and cannot prove causation. On the other end of the spectrum, if the study is overly controlled, it leaves little application to real world scenarios where life is not controlled. I do not mean to be overly critical of the scientists performing these studies, as they are doing their best with the scientific tools they have available. I do, however, mean to be critical of the news agencies and so called experts on social media who promote these studies as if they have definitively answered the questions we have all been asking. The reality is far from it.
The first study (Nutrition and Diabetes 2016,6,e218) examined over 23,000 people in two different epidemiological studies (Moli-sani and INHES trials) and concluded that eating pasta is not associated with increased body weight or abdominal obesity. This is the study we have all been waiting for, right? Now we can get the big heaping bowl of pasta and feel good about ourselves. Who doesn’t want that?
It did not take long for the headlines to roll in. “Eat Pasta to Lose weight!” Or, “Think Pasta is fattening? Think again! It may help you lose weight!” And may others. But my favorite is definitely from “food.mic” and their headline, “This study on how pasta can help you lose weight is easily the best science of 2016.” Gag. It could be nominated for the worst science of 2016. How they can be so far off base is beyond me.
For starters, this wasn’t actually one study. Instead, the report took data from two different studies and compared them. One study, the INHES group, reportedly only filled out a single survey of their food consumption in a 24-hour period, and the body weight and height measurements were self-reported (definitely subject to creative reporting by the subjects). That hardly seems like an accurate assessment of their health and dietary patterns. The other study, the Moli-Sani group, also had just one data point of dietary patterns and was very subject to recall bias.
The next problem is that the authors try to make adjustments for variables, but as we have seen before, there is no way to compensate for all the variables. For instance, those who ate pasta were also more likely to follow a Mediterranean diet (which has been proven to reduce cardiovascular outcomes, reduce weight, and improve biomarkers). So was it really the pasta that helped the subjects maintain a lower BMI? Or could it have been that they ate more in line with the Mediterranean diet? We do not know. This study does nothing to prove that point.
Other key points I enjoyed learning: 1- A “large” portion of pasta in Italy is 3 ounces. That is barely an appetizer in the U.S. Therefore this would not be applicable to anyone who thinks an overflowing bowl of pasta is a normal portion. 2- The study was funded by Barilla, the pasta company. Do you think they had an agenda going into the study?
Despite all that, no study is completely devoid of useful information. We can conclude that pasta is not inherently evil, and one bite will not cause you to gain weight and erode your health. When pasta is a small part of an otherwise balanced and healthy diet, it could be fine. The problem for many Americans is that we like extremes. If some pasta is good, then the endless bowl of pasta and Olive Garden must be great! For those of us who gravitate toward extremes or have difficulty with self-control, I would still suggest avoiding pasta. For those who are better at regulating portion sizes and balance (trust me, this is a skill that needs practice), pasta can be part of an enjoyable lifestyle.
As always, the main conclusion is: Don’t believe the hype! We need to take the time to understand what is behind the hype, understand the positives and negatives of the study, and understand how it may apply to us as individuals and as a society.
The second study (American Journal of Clinical Nutrition 2016 doi: 10.3945) investigated the hypothesis that a very low carbohydrate diet can increase calorie utilization and fat burning. The theory is that carbs increase insulin levels, which act as a fat storage hormone. Insulin will then cause an increase in fat stores, thus reducing the number of calories our bodies burn at rest, ultimately leading to weight gain. Switching carbs for fat should therefore have the opposite effect. A low-carb diet will lower insulin, increase fat utilization, increase resting metabolic rate, and aid in weight loss.
This trial enrolled only 17 overweight subjects. They were sequestered in a metabolic ward where their metabolic rate was accurately measured and they were monitored for their activity level and food intake. They ate only the food that was provided, and their every movement was observed.
This study is in direct contrast to the pasta study I mentioned earlier. The pasta study had no controls, no causative proof, and far too many variables. This study, on the other hand, probably went too far in controlling the environment. That level of control was necessary to isolate a single variable, a high fat compared to a high carb diet. In the end, they concluded the low-carb diet may have less of a metabolic effect than some have promoted. However, what I find fascinating, is that the low carb diet DID lead to weight loss, it DID increase resting energy expenditure, it DID reduce insulin, triglyceride and leptin levels. Yet the researchers claimed it proved a low-carb diet was not truly beneficial. To me, this highlights the importance of bias in interpreting the results. The authors seemed to have a bias against a low-carb diet, so they interpreted the findings by stating how the low-carb diet should have shown even greater effects than it did. Let me get this straight. It showed the exact effects you were testing it for, but you felt it should be a greater effect and therefore you call it a negative study? Sounds fishy to me.
In addition, as we explore the details of the study, we see even more reasons to be skeptical of the publicized conclusions. The subjects were followed for only 4 weeks on the low-carb high-fat diet. There is a well-described adaptation period to a high-fat diet, so this study barely got out side of that time frame. Also, one of the main reported benefits of higher fat diets is that even without purposefully calorie restricting the subjects, they still consume fewer calories then those on a calorie restricted low-fat diet. The higher fat diet is more filling, and therefore they can control their cravings and eat less. This is vitally important in the real world setting, but it is something this trial could not assess given the overly controlled environment.
Lastly, and this is my favorite, for the first 4 weeks the subjects were given a high carb diet that was supposed to match what they were eating prior to enrolling in the study. What happened? They lost weight right away! That tells me 1- The subjects were way off when they said how much and what they ate at baseline. 2- The “high carb” diet given to the subjects wasn’t representative of the standard American diet that most people eat. They did specify in the trial that the high-carb diet they provided was low in processed foods and added sugar. So even though this diet was supposed to be the high carb, high sugar diet that most Americans eat, it was still a dramatic improvement over what they were really eating. Therefore, the study comparison should not have been the high fat diet with the high carb study diet, but rather the high-fat diet compared to the pre-enrolment diet. That likely would have shown the much more dramatic benefits the authors were looking for.
Regardless, the study does raise the potential that the physiological effect of a very low-carbohydrate diet may not be as great as promoted by it’s most vigilant supporters. One big problem, however, is that this trial is so far outside the realm of the real world that it has little application to our lives. Once again, however, there is still useful information to be gained from this study. The take home messages should be:
- Eliminating processed food and added sugar resulted in weight loss and health improvements even when they were still eating a high-carb diet.
- Switching to a low-carb, high-fat diet resulted in additional weight loss, reduced insulin levels, reduced leptin levels, reduced triglycerides, and an increase in the resting energy expenditure.
Clearly a low-carb, high fat diet could be a useful diet for some people to help with weight loss, satiety and reduce cravings. Is it for everyone? Of course not. The key is finding a nutritional pattern that we can follow long term that helps promote a healthy weight, supplies adequate nutrition, and is enjoyable. That may or may not include appropriate portions of pasta. It may or may not be a high-fat low-carb diet. But it definitely should be a low-processed foods and low-added sugar diet. At least on that we can all agree.
Thanks for reading.