Can Eating Pasta Really Help You To Lose Weight?
By Dr Catriona Walsh
Recently headlines about pasta being able to aid weight loss might have caught your eye. Pastafarians (and other wheat worshippers) all over the world rejoiced, having heard the wonderful news, delighted that huge guilt-free plates of pasta were back on the menu again. For most it was probably more about assuaging guilt over devouring pasta, rather than a behavioural change that was most important here. No more tears shed over a great big plate of spaghetti or lasagne.
Some people were understandably confused, given that every week there seems to be a contradictory new nutrition study. That’s where it comes in handy to have some training in critiquing research. Having your research published in a peer reviewed journal is certainly not a guarantee that your findings are reproducible, or that your research is any good. So without further ado, let’s take a deeper dive into the most recent nutrition study that has had journalists tongues wagging.
The study, entitled “Effect of pasta in the context of low-glycaemic index dietary patterns on body weight and markers of adiposity: a systematic review and meta-analysis of randomised controlled trials in adults” was published in the BMJ Open on 2nd April 2018, and can be accessed here The supplementary materials are the most illuminating part of the study.
This study claims to be a meta-analysis and systematic review of low glycaemic index (GI) diets. Study authors are deeply involved and invested in the diet and food industries, including Glycaemic Index Laboratories, Toronto, The International Carbohydrate Quality Consortium, many nut, peanut and dried fruit councils, soy associations, Pulse Canada, the International Life Science Institute (ILSI) North America (ILSI are lobbyists for large food companies and their trade associations, such as Burger King, Kellogg’s, Coca-Cola, Heinz, and others), and many, many august professional healthcare and nutrition bodies; far too many to list here. But you can read the full list of competing interests in the study itself. Suffice to say the authors are a group of some of the most powerful and influential players in the world of nutrition, are inextricably linked with Big Food, and have their fingers in many (almost exclusively plant-based) pies.
Funding for this study was from various government, university and diabetes bodies, as well as clinical research facilities linked to St Michael’s Hospital, Toronto. This study did not receive direct funding from food corporations. However, a number of the individual studies which this study reviewed did receive funding or foods from companies such as Unilever, Cereal Partners UK, Weetabix, The British Heart Foundation (who absolutely love a low fat high carb study or 2; the more “heart-healthy-whole-grains” the better), The International Olive Oil Council and The Canadian Diabetes Association (another organisation well known for its proclivities towards low fat guidelines). This is just a small selection of some of the funding and food sources, but the full list is considerably longer.
The study authors searched for randomised controlled trials where people were placed on diets with different glycemic indexes. These were not studies looking at whether a low fat or high fat, or a low carb or high carb diet is better. The protein content was occasionally also changed, so some groups went on to a high protein, low GI diet. The main outcome the authors were concerned with was whether “low GI” diets resulted in better outcomes than “high GI” diets.
That is to say that the study authors wanted to know whether eating large amounts of refined carbohydrates, eg those found in white bread, potatoes, and white rice were associated with less weight loss than low GI foods, such as wholegrain foods like porridge oats, pulses like lentils and chickpeas, fruits and vegetables, and even pasta.
Another way to say it would be that people on a low GI diet would be eating more whole foods, vegetables, wholegrains and fibre, more naturally occurring vitamins and minerals and plant phytonutrients present in real food, and less processed foods (including less sugar, wheat, refined flour, white rice and potatoes and foods made from them, which also often contain vegetable oils and trans fats as well as food additives).
Or another way to word it would be that people eating low GI foods would have been more encouraged to cook their own food, or at least use less processed foods and ingredients, while those on a high GI diet would be more interested in their macros than in the food quality. After all, isn’t it easier to buy scones and low fat crisps than to make those sorts of items from scratch? Participants in the high GI arms of the studies might not have been eating scones and low fat crisps, however the meta-analysis tells us absolutely nothing about what anyone ate, apart from pasta, so you cannot assume that they didn’t eat more discretionary foods either. Which brings me on to my next point.
Although the study purported to investigate pasta, there were no studies at all where pasta was the only food that was changed. That is to say that no randomised controlled trials investigated whether or not eating any pasta, or whether altering the amount of pasta you eat, alters weight loss. Pulses and vegetables are both very important low GI foods, and their intake was not analysed in this study at all (although the study gives the reader an impression that the main change made was an increase in pasta).
32 trials involving 2448 participants were analysed. The effects of a "low GI" (official definition of a low GI diet is a GI ≤55) compared with a "high GI" diet (official definition of a high GI diet is >69) were compared for body weight (all 32 trials), BMI (18 out of the 32 trials), waist circumference (18), body fat (10), waist-to-hip ratio (6), and sagittal abdominal diameter (3 trials). None of the participants had a normal or low BMI (<25) at baseline.
Out of the 32 trials included, only 11 (about 1 in 3) actually quantified the amount of pasta consumed. The average for those 11 trials was a pretty paltry 3.33 servings per week, with a range of 1.75-7 servings a week. In other words, we don't know how much pasta people wer eating in the study, but we suspect it's probably only a serving every couple of days, and very unlikely to be more than 1 serving per day. But, to be perfectly honest, they are super vague on how much pasta people were eating.
Also of the 32 trials only 7 trials actually had participants on a truly high GI diet in either arm.
Image byJorge Zapata
Recently headlines about pasta being able to aid weight loss might have caught your eye. Pastafarians (and other wheat worshippers) all over the world rejoiced, having heard the wonderful news, delighted that huge guilt-free plates of pasta were back on the menu again. For most it was probably more about assuaging guilt over devouring pasta, rather than a behavioural change that was most important here. No more tears shed over a great big plate of spaghetti or lasagne.
Some people were understandably confused, given that every week there seems to be a contradictory new nutrition study. That’s where it comes in handy to have some training in critiquing research. Having your research published in a peer reviewed journal is certainly not a guarantee that your findings are reproducible, or that your research is any good. So without further ado, let’s take a deeper dive into the most recent nutrition study that has had journalists tongues wagging.
The study, entitled “Effect of pasta in the context of low-glycaemic index dietary patterns on body weight and markers of adiposity: a systematic review and meta-analysis of randomised controlled trials in adults” was published in the BMJ Open on 2nd April 2018, and can be accessed here The supplementary materials are the most illuminating part of the study.
This study claims to be a meta-analysis and systematic review of low glycaemic index (GI) diets. Study authors are deeply involved and invested in the diet and food industries, including Glycaemic Index Laboratories, Toronto, The International Carbohydrate Quality Consortium, many nut, peanut and dried fruit councils, soy associations, Pulse Canada, the International Life Science Institute (ILSI) North America (ILSI are lobbyists for large food companies and their trade associations, such as Burger King, Kellogg’s, Coca-Cola, Heinz, and others), and many, many august professional healthcare and nutrition bodies; far too many to list here. But you can read the full list of competing interests in the study itself. Suffice to say the authors are a group of some of the most powerful and influential players in the world of nutrition, are inextricably linked with Big Food, and have their fingers in many (almost exclusively plant-based) pies.
Funding for this study was from various government, university and diabetes bodies, as well as clinical research facilities linked to St Michael’s Hospital, Toronto. This study did not receive direct funding from food corporations. However, a number of the individual studies which this study reviewed did receive funding or foods from companies such as Unilever, Cereal Partners UK, Weetabix, The British Heart Foundation (who absolutely love a low fat high carb study or 2; the more “heart-healthy-whole-grains” the better), The International Olive Oil Council and The Canadian Diabetes Association (another organisation well known for its proclivities towards low fat guidelines). This is just a small selection of some of the funding and food sources, but the full list is considerably longer.
The study authors searched for randomised controlled trials where people were placed on diets with different glycemic indexes. These were not studies looking at whether a low fat or high fat, or a low carb or high carb diet is better. The protein content was occasionally also changed, so some groups went on to a high protein, low GI diet. The main outcome the authors were concerned with was whether “low GI” diets resulted in better outcomes than “high GI” diets.
That is to say that the study authors wanted to know whether eating large amounts of refined carbohydrates, eg those found in white bread, potatoes, and white rice were associated with less weight loss than low GI foods, such as wholegrain foods like porridge oats, pulses like lentils and chickpeas, fruits and vegetables, and even pasta.
Another way to say it would be that people on a low GI diet would be eating more whole foods, vegetables, wholegrains and fibre, more naturally occurring vitamins and minerals and plant phytonutrients present in real food, and less processed foods (including less sugar, wheat, refined flour, white rice and potatoes and foods made from them, which also often contain vegetable oils and trans fats as well as food additives).
Or another way to word it would be that people eating low GI foods would have been more encouraged to cook their own food, or at least use less processed foods and ingredients, while those on a high GI diet would be more interested in their macros than in the food quality. After all, isn’t it easier to buy scones and low fat crisps than to make those sorts of items from scratch? Participants in the high GI arms of the studies might not have been eating scones and low fat crisps, however the meta-analysis tells us absolutely nothing about what anyone ate, apart from pasta, so you cannot assume that they didn’t eat more discretionary foods either. Which brings me on to my next point.
Although the study purported to investigate pasta, there were no studies at all where pasta was the only food that was changed. That is to say that no randomised controlled trials investigated whether or not eating any pasta, or whether altering the amount of pasta you eat, alters weight loss. Pulses and vegetables are both very important low GI foods, and their intake was not analysed in this study at all (although the study gives the reader an impression that the main change made was an increase in pasta).
32 trials involving 2448 participants were analysed. The effects of a "low GI" (official definition of a low GI diet is a GI ≤55) compared with a "high GI" diet (official definition of a high GI diet is >69) were compared for body weight (all 32 trials), BMI (18 out of the 32 trials), waist circumference (18), body fat (10), waist-to-hip ratio (6), and sagittal abdominal diameter (3 trials). None of the participants had a normal or low BMI (<25) at baseline.
Out of the 32 trials included, only 11 (about 1 in 3) actually quantified the amount of pasta consumed. The average for those 11 trials was a pretty paltry 3.33 servings per week, with a range of 1.75-7 servings a week. In other words, we don't know how much pasta people wer eating in the study, but we suspect it's probably only a serving every couple of days, and very unlikely to be more than 1 serving per day. But, to be perfectly honest, they are super vague on how much pasta people were eating.
Also of the 32 trials only 7 trials actually had participants on a truly high GI diet in either arm.
- The majority of participants in the so-called "high GI" arm of individual trials were on a moderate GI diet (55-69).
- A few trials had the "high GI" participants on what was really a low GI diet, and those on the "low GI" diets were really just on an even lower GI diet (so effectively comparing 2 different low GI diets).
- In a few of the trials the participants who were supposedly in the "low GI" arm were actually on moderate or even high GI diets.
- Several trials compared 2 moderate carbohydrate diets with slightly different GIs and called the lower one "low GI" and the higher one "high GI".
On top of all that, the carbohydrate content of various studies varied greatly, ranging from just 36.2% (so what would probably actually be classed as a mild low carbohydrate diet since the carbohydrate content was <40%) right up to 68%. For each individual study the participants in the different GI groups had fairly similar macros, with the exception of a single study that used Canola oil as an ingredient in bread to reduce the GI and consequently to also reduce the carbohydrates and increase the fats. However there were absolutely no standard macro ratios across all the various studies.
The same thing occurred for proteins: most diets had a moderate protein intake for both arms, but protein intake between studies ranged from 13.3%-28.3%, which is actually quite a high protein diet at the upper end of the range.
Fats ranged from 16% right up to 40%, which is more than a twofold difference. In addition, some participants were on calorie restricted diets, while in other trials participants were allowed to eat as much as they felt like, so long as they obeyed the rules about which foods were allowed and which were off limits or should be limited. In some trials foods were supplied by industry sponsors. In others the participants had to supply everything themselves.
So in this meta-analysis is becomes very difficult to work out whether any differences you see in parameters like body weight and BMI are because of a reduction in GI, a difference between carbohydrate content, a difference between dietary fat amounts, a difference in protein content, or just a reduction in the exposure to processed foods and/or wheat and gluten, or an increase in vegetables like legumes and starchy vegetables (apart from potatoes). It would be impossible to ascertain whether any differences between groups was due to pasta intake, and the authors never actually do this; they just make it sound like pasta aids weight loss as part of a "low GI" diet, by which they mostly really mean a moderate GI diet.
Statistical witchcraft nevertheless somehow managed to take this hodgepodge of rather different trials and pretend that there was some sort of standardisation going on which would allow them all to be analysed together. The results, shown in the forest plot diagram below, reveal a pretty measly reduction in body weight of only 0.63kg for the "low GI" group compared with the "high GI" group.
The next image from the study is of the effect on body weight, BMI, body fat, waist circumference, waist-to-hip ratio, and sagittal waist diameter. The reduction in body weight seen with the low GI diet was echoed by a reduction in BMI. However, % body fat, waist circumference, waist-to-hip ratio and sagittal abdominal diameter did not change.
What on earth is going on here? The study authors did not attempt to explain this, so your guess is as good as mine. They made mention of the fact that the quality of the evidence for waist circumference and body fat % were graded as low, so perhaps they just felt that this part of the study was less reliable than the rest of this faux "pasta aids weight loss" study, and it wasn't worth discussing the fact that participants did not reduce their body fat % or waist circumference on a "low GI" diet compared with those on a "high GI" diet. Alternative hypotheses could include that the unimpressive amount of body weight lost was actually protein from muscle, or bone density, but those risks were not assessed at all.
This meta-analysis gives the impression it is able to address a question about whether pasta has an effect on weight loss and adiposity. The study clearly doesn't really answer any questions on whether eating pasta has any effect on weight or adiposity, because none of the trials it analyses sought to address that specific question.
To summarise; a meta-analysis performed by a group of luminaries, inextricably linked with the food industry and with an interest and with an interest in low fat high carbohydrate diets, showed that if you are an overweight or obese (non-pregnant and not lactating) adult, and you eat a diet which includes carbohydrates, and are advised to try to reduce the GI of your food (an unknown proportion of which may or may not be pasta) by some vague and extremely wide ranging amount, you might possibly lose about 0.63kg of body weight compared with someone eating an equal amount of carbohydrates made up of white rice, potatoes, white bread and cereals. But you won't know whether any of the weight lost is actually body fat. Underwhelmed? If you are, you are surely not alone.
This study does not address questions like:
Statistical witchcraft nevertheless somehow managed to take this hodgepodge of rather different trials and pretend that there was some sort of standardisation going on which would allow them all to be analysed together. The results, shown in the forest plot diagram below, reveal a pretty measly reduction in body weight of only 0.63kg for the "low GI" group compared with the "high GI" group.
The next image from the study is of the effect on body weight, BMI, body fat, waist circumference, waist-to-hip ratio, and sagittal waist diameter. The reduction in body weight seen with the low GI diet was echoed by a reduction in BMI. However, % body fat, waist circumference, waist-to-hip ratio and sagittal abdominal diameter did not change.
What on earth is going on here? The study authors did not attempt to explain this, so your guess is as good as mine. They made mention of the fact that the quality of the evidence for waist circumference and body fat % were graded as low, so perhaps they just felt that this part of the study was less reliable than the rest of this faux "pasta aids weight loss" study, and it wasn't worth discussing the fact that participants did not reduce their body fat % or waist circumference on a "low GI" diet compared with those on a "high GI" diet. Alternative hypotheses could include that the unimpressive amount of body weight lost was actually protein from muscle, or bone density, but those risks were not assessed at all.
This meta-analysis gives the impression it is able to address a question about whether pasta has an effect on weight loss and adiposity. The study clearly doesn't really answer any questions on whether eating pasta has any effect on weight or adiposity, because none of the trials it analyses sought to address that specific question.
To summarise; a meta-analysis performed by a group of luminaries, inextricably linked with the food industry and with an interest and with an interest in low fat high carbohydrate diets, showed that if you are an overweight or obese (non-pregnant and not lactating) adult, and you eat a diet which includes carbohydrates, and are advised to try to reduce the GI of your food (an unknown proportion of which may or may not be pasta) by some vague and extremely wide ranging amount, you might possibly lose about 0.63kg of body weight compared with someone eating an equal amount of carbohydrates made up of white rice, potatoes, white bread and cereals. But you won't know whether any of the weight lost is actually body fat. Underwhelmed? If you are, you are surely not alone.
This study does not address questions like:
- can eating pasta help me lose weight?, since zero of the studies attempted to look at that question
- is eating a high carbohydrate diet better at helping you reach a normal weight than eating a low carbohydrate diet?, since the only study even attempting to half address this was a study on using Canola oil to reduce the glycaemic index, which was sponsored by the Canola Council of Canada
- is eating a low GI diet superior to eating a low carbohydrate or high protein diet at helping you reach your optimal weight?, since zero of the studies attempted to look at that question
- is it safe to eat pasta frequently long term as part of any diet (ie will eating pasta affect the age at which I die, or my risk of developing any illnesses, if I continue to eat pasta frequently for many years)?, since zero of the studies attempted to look at that question.
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