ARE CARBS MAKING YOU FAT?
There has to be good reason for why sayings like “No carbs before Marbs” became famous right?
Every week you hear of a new celebrity that has gotten into top shape by following some kind of a low carb diet. So, with the aim of getting abs for summer, should we all be avoiding carbs like the plague? This article cuts through an enormous stockpile of scientific evidence to answer the carb conundrum once and for all…
Of course, there always has to be a big bad villain in any story worth reading… but when it comes to carbs and real life, is it really that simple?
Since this is such a HUMONGOUS topic and a very long article, I have decided to first summarise my findings and conclusion for those of you that don't like reading. However, for those of you that like to know why and are partial to a bit of science, then feel free to join me throughout the rest of the article in my journey to uncover the truth.
Scientific evidence routinely presents an inconsistent message when it comes to the carb debate. Therefore, I have near sent myself crazy (or should I say crazier than I am…), trying to maintain an open mind as I studied a mass of research looking at it from every angle.
To briefly summarise the findings, there are studies that show a short-term advantage to following a low-carb diet, yet those spanning a year of more seemingly show no difference in weight-loss between low- or high- carb dieters. There are also studies that show that extremely high-(70% carbs) carb diets can offer a weight-loss advantage over average-carb diets. Then there’s the ‘gold standard’ metabolic lab studies, which show low-fat dieters lost significantly more fat than the low-carb dieters. And that is despite the fact that they’re bodies were showing to be burning more fat for fuel, and that they’d initially lost more weight.
You can also see from the studies that compare the efficacy of the most popular diets, that it doesn’t actually matter what kind of diet people follow, overall they will still have lost the same amount of weight by the time they get to 12 months.
Furthermore, there are studies that show that overfeeding on carbs makes you no fatter than overfeeding on fat, and that eating crappy, sugary high-GI carbs (carbs that have a high glycaemic index such as sugary processed foods) has no short-term effect on your weight-loss efforts. Although, when you look at the longer studies, you find that the quality and GI rating of the carbohydrates that you consume is likely to play a significant role in weight-gain over time.
In view of all of the studies that I have scrutinized (and there were soooo many more than I have reviewed here!) I do not believe that carbs are the villain that they have been made out to be.
It would seem that most people can lose just as much weight (and possibly even more fat) on a moderate- or high-carb diet as they can on a low-carb diet, and that the operative word here is diet. I.e. those that stick to a diet will lose weight regardless of the inclusion of carbs.
Although, the optimum amount, and kind of carbs eaten, will differ greatly from person to person; it seems that for most healthy* individuals, including a variety of the more healthful natural carbs, in a balanced diet, is an effective strategy for achieving and maintaining a lean, healthy body. Especially more fruits, veggies and wholegrains as shown in the enormous study that spanned 20-years and included over 120,000 people!
Moreover, if including carbs in your diet improves your mood and quality of life, then it will increase the likelihood that you adopt these goal-supportive eating behaviours into a new long-term lifestyle, to keep the weight off for good.
On the flip side, if you personally find that by eating a low-carb diet, the quality of your diet improves (and you enjoy it), then this too is an effective weight-loss strategy.
Just make sure that you embark on a diet that suits your health-status, likes, and lifestyle. After all, you are a product of your small daily habits, so consistency will ultimately determine your fat-loss success!
So, to answer to the question of ‘are carbs making you fat?’; I’d say that this is only the case if you have a health condition that prevents their proper metabolism, or you are abusing them overall (eating way too many and eating lots of processed junk, over a long period of time).
Rather, I believe that it is the overall amount of food you eat, in what balance, along with the quality of food you regularly consume, all in relation to your health-status and activity level, that actually determines how fat you do or don’t get. PHEW!
Now to get into the ‘why’s’ and science… and goodbye and thank you for reading to those that have had enough ;)
HOW COULD CARBS INCREASE FAT?
To answer the question of are carbs making you fat, it makes sense to explain why carbohydrates have been vilified in the first place.
Carbohydrates are an efficient energy source that provides vital fuel to every cell in your body, in the form glucose. The value of glucose is highlighted by the fact that even in the absence of eating carbohydrates, your body will manufacture it from proteins and fats through a metabolic pathway called gluconeogenesis. This also shows that you do not need to specifically eat carbs to provide your body with glucose.
When eaten, carbs increase blood sugar levels and this elicits an insulin response. Although, to be clear, protein also does this to a far lesser extent. Warning, this is the pivotal part in the story in which the big bad carb villain is revealed!
Insulin is widely understood to be the hormone that makes you fat. In reality, insulin is just the chemical equivalent of a switch that simply shifts you between the two modes of metabolism (fat or glucose utilization). In healthy* individuals, this switch efficiently enables you to make the most of the foods that you consume and maintain balanced blood glucose levels.
Of course, it makes perfect sense that our body was designed to effectively use whatever food sources are available to us, as back in the days of the saber-toothed tiger there might have been nothing but berries to eat one day and then a whole feast of a wild animal the next.
Basically, when you eat a meal high in carbs, insulin switches your body into ‘glucose utilization mode’ so that you use up that glucose for energy whilst also restoring up your energy stores found in your muscle, liver and fat cells. None of which makes you any fatter! Fat storage is only promoted when there remains an excess of glucose left over. Although, it is also fair to point out that this is the case when there is an excess of food in general.
It’s also important to know that insulin is your muscles best friend because it’s job is to halt muscle breakdown, shuttle amino acids into your muscle cells and turn on protein synthesis. Thus, insulin is your anabolic super-agent that builds more muscle tissue! And remember, whether or not you are simply aiming to tone up a little, or give Hulk Hogan a run for his money, by increasing your lean tissue mass, you burn more calories just by being alive.
On the flip side, insulin gets it’s bad name since whilst in action of muscle building, it switches over fat metabolism to carb metabolism. This temporarily inhibits fat burning and promotes the synthesis of triglycerides (the precursor of fat) in fat cells. So, during the time in which your insulin is high, you are not burning away your excess body fat.
To be clear, you cannot be building muscle and burning fat at the exact same time and so your body rapidly shifts between modes to optimise what you feed it. This is why athletes manipulate the amount of carbs that they consume at different times in the day. They are cleverly taking advantage of the muscle building and energy storage benefits of insulin.
In healthy* individuals, the insulin switch is a highly efficient process that shifts you back into ‘fat burning’ mode once the glucose has been put to good use. As with everything, problems only arise when you get too much of a good thing!
With that in mind, let’s now look at what science has to tell us about eating carbs and getting fat!
REVIEW OF THE SCIENTIFIC EVIDENCE
P.s. I want you to know that I did not go into this research being either a carb advocate nor a carb loather. I have always been sat on the fence, seeing truth and logic on both sides and believing that this will depend upon the individual and their specific lifestyle, body type and condition of health. Therefore, I went into this with and inquisitive and open mind about what I might find, always hopeful to uncover the truth and make sense of the ongoing controversy. You may sense my overall opinion as you read through my take on these studies, but remember that I am writing this after having already gone over it all and come up with my conclusions…
How do low-carb diets fair?
Let’s first begin with a recent meta-analysis (1) that pooled together the data from 11 randomised controlled trials, lasting 6 months or more, that compared low-carbohydrate diets (less than 20% carbs in this case) to low-fat diets. The study included data from 1369 healthy participants and they found that there was a mean 2kg weight loss advantage to those following the low-carbohydrate diet. However, they also found that those following the low-carb diet also presented with increased low-density lipoprotein (i.e. bad cholesterol and thus bad news). Please also note that this study measured weight loss and not ‘fat loss’, which (as you will see later on), can give the results a different meaning.
Then there is a gold standard, tightly controlled study (2) in which participants were admitted into a metabolic ward for the duration of the experimentation. This found that more body fat was lost as a result of following a lower-fat diet in comparison to a low-carbohydrate diet. Interestingly, this study also found that the low-carb group showed an increase in fat-burning for fuel, yet during those 2 weeks they lost less body fat.
Since this study was so well designed, it is difficult to pick it apart and question its conclusions, but to be open to misrepresentation, it is fair to mention that each diet only lasted for 2 weeks and there were only 19 participants. This means that things may look very different had it have gone on for much longer and involved many more people.
Another study (3) on 33 severely obese subjects found a significantly greater reduction in BMI in those following a low-carb diet to those following a low-fat diet. Interesting, this study began with 46 participants, but as is commonly seen with dieting research, only 33 of them lasted the entire study. This in itself is speaks volumes, as it clearly highlights that dieting in general seems to be very problematic for most, regardless of what kind of diet they are following!
Getting back to the results, although they found that initially the lower carb group lost more weight, at 9-months the weight loss was the same for both diet groups.
Then there is a 6-month diet comparison study (4) that looked at the advantage of a very low-carb diet (less than 20g carbs) to a reduced-calorie, low-GI diet (cutting out high sugary foods, white bread, potatoes etc) and again, they found that there was more ‘weight’ lost on the very low-carb diet.
However, the ‘very low-carb group’ were restricted to only meat, cheese, eggs and 3 cups of non-starchy veggies a day! Calories were not monitored this group, and I believe that it is quite possible that calories could have dropped significantly due to being so little choice in food. As we might expect, only 59% of the participants saw the study through to the end… hmmmm dieting really does seem to be quite a problem and I’m sure many of you can relate to this, as I know I certainly can! Also, the study only lasted 6 months, so based on previous studies, who is to say that there would be any difference 3 months later?
One study on the Atkins diet (5) found that participants initially lost 4% more body weight than the higher carb dieters, but that there was no difference between diets at 12 months. There seems to be a pattern emerging here with carbohydrate restriction having no advantage after a certain period of time… Even if it were possible that it had nothing to do with carbohydrates and was actually a result of people not adhering to their strict diet past the 6-month mark, then this again shouts out that restrictive diets are not sustainable for life. Again, I think we can all relate to this. Cabbage diet anyone?
Trying not to bore you to tears, there are many more published large meta-analysis studies (6, 7, 8, 9) that show that there is no weight-loss difference between those following a low-carb diet, to a higher-carb diet. Similarly, there are highly controlled shorter 6-weeks studies (10, 11) that also found no weight-loss advantage to going on a low-carb diet.
To finish off with the low-carb evidence, we now look at a recent study (12) that is thought to be one of the very best dietary studies carried out to date. This lasted 8 weeks and was run by the well-respected; Keven Hall, in the same metabolic lab setting previously mentioned. Again, there were only 17 participants, but this time they compared a keto diet (30g of carbs a day) to a high carbohydrate diet (300g of carbs a day). Yes, that is 10x as many carbs in the high carb group! As in their previous study, those on a low-carb diet adapted to it by switching to the metabolism of fat for fuel. They also found that the keto dieters experienced a slight increase in metabolic rate and burned around 100 more calories a day.
Furthermore, they initially lost ‘double’ the amount of weight than those on the high carb diet… but this weight loss slowed as the diet continued. And, shockingly most of it was water, some of it was a loss of lean mass (muscle) and they actually lost half of the amount of body fat than the high carb dieters! This study again shows that the body cleverly adapts to burning what it is given for fuel, but actually being ‘fat adapted’ does not necessarily offer an advantage to loosing body fat. In fact, in this study, it correlated with loosing less body fat and it was the high-carbohydrate diet that was most effective for this purpose.
What about comparing popular diets?
There have been various studies that seek to find the most effective weight loss diet (13, 14, 15) and yet it appears that they each report no difference between the weight lost by participants on any of the diets at 12 months. One of these (13) compared Atkins (low-carb) to Ornish (low-fat) and Zone (macro balanced) diets in overweight postmenopausal women. Another (14) that compared the results of popular diets with 7,286 participants, found that Atkins presented with the most potential at 6-months, but then there was no difference at 1 year.
Interestingly, the third study (15) found that although they deemed there to be no significant difference between the weight lost from diet to diet, Atkins dieters lost the least amount of weight in 12 months, and the low-fat diet lost the most. The researchers also asked participants to honestly report their adherence to the diet and they concluded far better adherence to the least restrictive diets (zone and weight watchers) in comparison to those that severely cut out down on a particular food group (Atkins and Ornish).
To throw a complete spanner in the carbohydrate works, a study on 40 males (16) comparing an Asian diet of very high carbohydrate (70% carbs and 15% fat) with a Western diet of moderate carbohydrates (50% carbs and 35% fat) found that the very-high-carbohydrate diet group lost significantly more weight, as well as improved inflammatory markers, reduced insulin levels and improved insulin sensitivity. The researchers suggest that the high-fat and low-fibre constitution of the western diet is likely to contribute significantly to these findings and it not just being about the carbohydrates.
Does overeating carbohydrates cause more fat gain than overeating fat?
One study (17) involving a mixture of lean and obese participants found that overfeeding subjects with carbohydrates resulted in much less ‘weight’ gain than overfeeding them with fat. On the other hand, another study (18) found no difference in ‘fat’ gain regardless of whether they were overfed carbs or fat. Either way, there is no evidence to suggest that carbs are any more likely to make you fat than anything else, rather it is about whether you eat more than your body needs.
What about the kinds of carbs eaten?
Considering that most carbohydrate studies are comparing ‘diets’, they are likely to be feeding their participants on the most healthful carbohydrate sources. Knowing this and the actions of insulin, it’s fair to question whether or not the more refined and/or sugary carbs are to blame for the nations expanding waistline. To be clear, the more refined and sugar carbs have a higher glycaemic index and load. The higher the glycaemic load, the higher the insulin spike since there is effectively more glucose for the body to mop up and use.
We will begin by looking at a 6-month study (19) on 32 individuals looking at whether or not the glycaemic load of the carbohydrates in a diet, affected the amount of fat lost. Researchers found that in healthy subjects the same amount of weight was lost on both the high- and low- glycaemic diets. However, those with insulin secretion problems lost more weight in the low glycaemic load diet.
Another larger 6-month study (20) on 398 subjects compared fat loss between those assigned to either a simple carb diet (high-GI and sugary) or a complex carb diet (low-GI, more fibre). They found no difference in fat loss between groups.
To test whether or not avoiding sugar is an effective diet strategy, a small 8-week study (21) compared weight lost on a low-sugar diet or a high-sugar diet. Surprisingly to the researchers, they found no difference in weight lost between groups and thus concluded that avoiding sugar was not an effective diet strategy.
The same story is evident even when looking at a much larger meta-analysis of randomised controlled studies that lasting between 3-6 months and included a total of 1,577 participants (22). There was no difference in weight lost between high- and low GI- dieters.
However, things may not be as clear cut as they seem! A 4-year study (23) on 2834 subjects found a positive correlation between high GI diets and the prevalence of metabolic syndrome. Thus, suggesting that over time, eating a diet high in refined and sugary carbs might damage the insulin/metabolic machinery, which may then lead to weight gain…
Surely enough, an observational study (24) that looked at 572 healthy participants over the course of a year found a positive correlation between body mass and the GI of carbs in the diet. That basically means that those eating the most high-GI foods were the heaviest. Although, it is also interesting to note that there was no association found between bodyweight and the amount of carbs eaten, which suggests that it is not eating ‘carbohydrates’ that makes you fat, rather eating too many of the less healthful ones that contributes to it.
What does the mother of all studies say on carbs?
Okay, so we have reviewed masses and masses of studies that look at the carb debate from every angle possible. However, always the sceptic, I wanted to include a huge study (25) that included over 120,000 people over 20 years! The participants were all free of chronic disease and not obese at the beginning of the study. Every 4 years the researchers evaluated changes in lifestyle factors and weight change. They didn’t specifically study carbohydrates, rather what factors affected or prevented long-term weight gain. Fascinatingly, they found that the 3 most strongly associated foods to weight gain were potato chips, potatoes and sugar-sweetened beverages. Conversely, the foods that were inversely related (i.e. those eating the most of these foods either lost weight or had the least amount of weight gain, if any) were fruits, yogurt, nuts, whole grains and vegetables. This again, highlights that carbohydrates in general are not the fat-causing villain that they have been made out to be, and actually it is more about the quality and quantity of food eaten!
SO, ARE CARBS MAKING YOU FAT?
Pooling all of this data together, the take home message is that if you are a healthy* individual, then carbs will not make you fat unless you overeat them (just like any other type of food), or your source of carbohydrates are primarily poor-quality, high-GI kind, over a long period of time.
So, if you are a healthy* individual and you enjoy carbs, then I would suggest including a good variety of the more natural carbohydrates into your meals for an effective fat-loss strategy. However, become familiar with portion sizes! Be mindful of your overall food level intake and balance out those carbs with enough protein, moderate fats and plenty of fruits and vegetables… along with staying active!
P.s. Do I eat carbs?
I have polycystic ovary syndrome, which is classed as a condition of pre-diabetes (which affects the efficiency of the insulin switch). Therefore, to keep my symptoms under wraps and me feeling fab, I get the majority of my carbohydrates from fruits, vegetables, and beans and pulses, rather than having lots of starchy carbs as my main meal staple. I have found that I feel much more vibrant eating this way.
Although, I do include things like unrefined rice, oats, sweet potato and root veggies in a number of meals throughout the week, as-and-when I feel like them and on high activity days. Some days I swap starchy carbs for more fruits, veggies and fats along with my protein, and on others I may have 2 or 3 portions of oats, sweet potatoes and rice (but I go with a small fist sized portion as part of a balanced meal).
However, let’s be clear, I am certainly not perfect! I do indulge in less-healthful foods like crisps, chips, pizza, cookies and sweeties like most people... The way I see it is that although they do not directly contribute to improving my physical health (quite the opposite!), they do certainly please me mentally and I am a staunch believer in a happy mind playing a huge role in a healthy body!
QUESTIONS & SUPPORT
If you have a question then please drop it into the comments box below as I would love hear from you. You can also let me know of any other topics that you would like me to cover in future blogs. Equally, if you found any of this article interesting then please share this on your social media channels to show your support and help me to grow my blog ;)
*Unhealthy individuals should seek professional independent nutritional advice from their medical practitioner as carbohydrates can play a key role in worsening certain conditions, such as diabetes and other metabolic conditions.