Low carbohydrate diets have been a popular staple on the fat loss scene for quite some time, and include some high profile company names, including Atkins and The South Beach Diet. They’ve overtaken low fat diets as the go to diet for weight loss.
However many of the low carb diets that are available are termed ‘fad’ diets that have little or no scientific backing. Sometimes this is justified. At other times it isn’t.
So I’ve been scouring the scientific journals from the past couple of decades to answer the question.
Fat Loss: To carb or not to carb?
The old school method: Low fat
Low fat diets do have a strong scientific backing for their effectiveness and clinically are the method usually advised to promote fat loss. However in the real world low carb diets have a far greater following. It’s likely this is due to low carb diets being able to offer faster results. In the long term though (up to and above 12 months) a low carb diet won’t be superior to a low fat.
Trials done with low fat diets, when combined with lifestyle adjustments such as exercise, have also shown to provide long term maintenance of weight loss.
Some argue that the best recommendation is to have a reduced calorie, low fat diet due to its beneficial effects on health risks, such as diabetes. This isn’t agreed upon for all health risks though. This is discussed more below.
Ok, so low carb diets are hocus pocus?
No. In fact over the initial 6 months low carb diets are shown to provide a greater fat loss. This wouldn’t be due to water weight loss as this is shown to be the same after the initial 2 weeks in a low carb and a low fat diet. With obese individuals the additional fat loss could be as much as an extra 3.9kgs in the 6 months. By 12 months after the diet was started however the difference between low carb and low fat is not significant.
This means that the claim that low carb diets allow you to lose weight faster does hold. It is very easy to dismiss the fact that the extra weight loss during the first couple of weeks is nothing but water. It is also very easy to prove as correct. Yet there is clear scientific evidence that a low carb diet will continue to allow you to maintain your increased weight loss past this and at least up to 6 months.
This isn’t the end of the story though. There are many other things to consider when choosing if low carb is right for you. One of the strongest factors is the likely hood that you will adhere to it. Evidence for low carb diet adherence is spotty. Some studies found that adherence to low carb diets was good. Other disagreed and stated that drop outs were high. It seems that motivation to continue was on the whole good for low carb. But the difference in adherence between low fat and low carb was usually minor (31-48% individuals on low carb verses 37-50% on low fat).
It appears fairly likely that the likelihood of you sticking to a diet depends on your preferences. If you like carbs (breads, fruit, pasta etc) then a low fat diet would be easier for you to stick to. Conversely if you enjoy your fats and protein (lean meats, fish, olives, nuts, eggs) then a low carb diet is the route for you.
What health implications does a low carb diet come with?
As with most things around nutrition different diets have different effects on different aspects of health. Some beneficial. Some detrimental. Low carb diets are no different.
Blood pressure is improved by eating a diet low in carbs. But the change is not different from the improvement seen in other diets after 12 months, such as low fat.
There is a large difference seen between low carb and low fat when cholesterol is analysed. Total cholesterol and low density cholesterol (LDL), aka the bad cholesterol, is reduced when you eat a low fat diet. Yet high density cholesterol (HDL), aka the good cholesterol, is increased on a low carb diet. Those on low carb diets did receive a reduction in LDL cholesterol too, but it was a lot lower. For this reason the correct path for yourself, if cholesterol is an additional focus, should be determined after having your blood analysed.
Blood pressure and cholesterol levels both tie strongly into your risk of cardiovascular disease. Although low carb diets will improve both of these factors it does come with the requirement that low levels of fruit, vegetables and whole grains are eaten. These are essential to your health, largely due to the high levels of quality vitamins and minerals the contain. In the long term this type of nutritional deprivation will lead to an increased risk of cardio disease. In the short term low carb diets do provide a reduction in cardiovascular problems, but the difference between it and other diets is not notable.
Low carb diets are often high in fat. Such diets are shown to increase the risk of certain cancers. If you do decide to opt for the low carb option though you can reduce your short term risk. Focus on choosing foods high in protein and unsaturated fats to replace the carbohydrates.
This focus on what’s replacing the carbs can also be seen when the risk of diabetes is considered. Diets that used high amounts of animal products, which are often high in saturated fats, showed an increased risk of developing type 2 diabetes.
So how many carbs equal low carb?
A low carb diet would have less than 45% of its energy coming from carbohydrates. For the average person this would be around 200 to 250 grams of carbs per day. However when diets are touted as low carb they are often restricting intake by far more than this.
The average intake in studies is between 79 and 97 grams of carbs each day. Extreme low carb diets have been as low as 8% of energy intake, or 46 grams per day.
The lower the carbohydrate intake the higher the likelihood of the effects mentioned above. The good, the bad and the ugly.
The hidden component. Protein.
As mentioned above where you are getting your other calories from can make a huge difference. This isn’t only health related though. Your ability to retain lean body mass, aka body weight minus body fat (so muscles, organs, blood vessels etc), is closely linked.
Recommended daily intake of protein is 0.8 grams per kilogram of body weight. Low carb diets though often contain a far higher intake. Studies show this to be beneficial. A protein intake of 1.2 grams per kilogram of bodyweight has been shown to allow an extra 0.96kg of lean body mass to be kept when compared to a group that ate 0.7 grams or less. This effect becomes more pronounced the longer the diet continues for.
This has the advantage of not only allowing you to maintain health and exercise ability, but will also increase the speed at which you lose fat. This is in part due to lean body tissue requiring energy, aka calories, to maintain it. The more you have the higher your metabolic rate will be. Another advantage is the higher satiety effect of protein, meaning that you feel fuller for longer when you eat more protein. This results in you eating less over a day.
When a high protein (30% fat, 25% protein, 45% carbohydrates) group was compared with a low protein (30% fat, 12% protein, 58% carbohydrates) group the high protein group lost an additional 3.3kgs of weight over a 6 month period due to them eating about 20% less calories per day. This is despite the fact they were not monitoring the number of calories they were consuming.
One study that was released recently stated that eating a very high amount of protein, at 2.4 grams per kilogram of bodyweight, whilst in a calorie deficit and when combined with very high intensity exercise would allow you to lose fat and build muscle at the same time. The study does have some flaws in its methods though, such as the sample size, or the number of people being tested, being small. Until further research is done this claim should be taken with a pinch of salt. It is also worth noting that very high intakes of protein may have a negative effect on the kidneys over time.
The main thing to take away from this review of the science is that when deciding how much carb is right for you the most important factor is personal preference. Studies show that over time individuals move back into eating their preferred macronutrient balance, even when a large and detailed support network is provided.
If you love porridge, or bread, or fruit, then a low carb diet isn’t going to work for you. You may lose a bit more weight by doing it granted. But if you quit within a few weeks then that extra weight loss will never materialise.
Part of this personalised diet choice should also take into account your specific health risks. If you need to increase your HDL cholesterol, or mitigate the risk of some cancers or diabetes, then in the short term a low carb diet could be beneficial. But the difference in most health factors when compared to other diets just doesn’t outweigh the downsides of a low carb diet in the long run.
If you do decide to use a carbohydrate restricted diet, then you need to pay close attention to what you are replacing those carbs with. Opt for plenty of protein and choose foods with unsaturated fats over saturated.
In any case it is ill advised to do a low carbohydrate diet for more than 6 months. Doing it for this period will result in slightly faster weight loss. But as you move past 6 months and up to 12 the difference between diets isn’t significant. So the side effects of a low carb diet completely outweigh the benefits. When you finish your low carb diet you can continue to lose weight by creating a calorie deficit, but focus on a more balanced diet.
I hope this has been a useful article and will aid you in making a decision when it comes to what diet is right for you. If you think others could benefit from it, please share it around. And if you have any questions just post them below.
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The boring references bit
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