The low carb approach to dieting is very popular. It is viewed as a good approach if you want to lose weight. But is it the right approach? Is it even an effective approach? In my view no. For a small number of people it might be the best approach, but for the vast majority there are better ways to lose weight.
Here I discuss my views on this popular approach.
I’m going to give you the answers upfront but if you’d like to understand the reasoning behind these points then you can read the rest of the article. So, in summary
- Low carb will help you lose some weight – a lot of it water – quite quickly, but then you are likely to plateau quickly and even gain body fat.
- Low carb will make it difficult to gain or hang on to muscle.
- Low carb will make you low in energy for your lifting workouts.
- Low carb will probably raise your cholesterol.
- You may not feel satisfied on a low carb diet.
- Low carb may make you miserable!
You can lose weight more effectively on a high carb diet, achieving better results in terms of body composition.
If you’d like to understand these assertions then read on…..
What is a low carb diet?
The UK Government recommends people should get at least 54% of calories from carbohydrate. The US Government says between 45% and 65%.
- For the average male burning 2500 calories a day, this represents 344g of carbs a day.
- For the average woman burning 2000 calories a day, this represents 275g of carbs a day.
With a low carb diet, carbs are kept well below these numbers. Some regard 150g a day as low carb, others say 100g a day is a good amount, but the purists will say that a proper low carb diet is ketogenic. Generally, you need to consume 50g or less per day of carbs to make the diet ketogenic.
What is a ketogenic diet? When carbs are as low as 50g you need to make up the calorie shortfall with protein and fat. Typically, a ketogenic diet will have 10% or less from carbs, 20-30% from protein and 60-70% from fat. After an acclimatisation period of a week or two on this kind of diet the body starts to produce ketones, which are a by-product of fat breakdown. Ketones provide an alternative fuel source, particularly for the brain which is usually carb-dependent. Once you are producing ketones, the argument goes, then you will be functioning normally if not better than those on a standard diet.
What’s the theory behind low carb?
The main argument for low carb dieting revolves around the hormone insulin. Insulin is released in response – mainly – to rises in blood sugar arising from carbohydrate digestion. Insulin is a potent ‘storage’ hormone. It will suppress lipolysis (fat breakdown) and stimulate lipogenesis (fat creation); it will shuffle carbohydrate and other nutrients in to storage in muscle and liver cells as well as suppressing muscle protein breakdown.
The argument goes that if you consume a lot of carbohydrate then your consequent regular insulin secretions will blunt lipolysis and prevent you from burning any fat. With a low carb diet insulin is kept to a minimum, allowing lipolysis – fat breakdown – to take place round the clock. So, the argument goes, on a low carb diet you’re going to burn a lot more fat and lose weight more rapidly.
Another advantage of the low insulin levels resulting from a low carb diet is that blood sugar will remain more stable. With a higher carb diet blood sugar will rise in response to eating, insulin will then drive blood sugar down and can lead to a blood sugar low which subsequently elicits hunger. This hunger can lead to overeating. With the low carb approach blood sugar is kept on a more even keel and hunger pangs become less frequent and less severe.
It all sounds reasonable, right? So, let’s look at some experiences of low carb dieting and examine a different diet approach so we can compare.
Experiences of low carb diets
I followed a ketogenic diet for a whole year, so I can speak with some authority on the experience. I know what you’re saying “If you’re not an advocate then why did you do that?”. Well it can look convincing on the surface and at the time I was still exploring approaches and seeing what worked.
Here’s a summary of my experiences
- I lost weight quickly initially.
- I plateaued quite quickly and then actually put on weight.
- Ultimately, I got fatter and lost strength and size.
- I lacked energy in my workouts.
- I struggled to get satisfaction from my food.
- Calorie control was more challenging because high fat foods pack a lot of calories and portion control has to be very precise.
I think the last two points are a reason why I put weight on. Let me assure you I am very motivated and strict when it comes to food, but even I found it a challenge. I should also add that my cholesterol levels went through the roof!
We have had clients come in for consultations saying similar things: “I was following a low carb diet which was fine for a while, I lost some weight, but then I plateaued.”
What’s going on there?
First, I think people lose weight quickly for two reasons
- When they cut the carbs they lose a lot of water that is stored with the carbs – three times as much water as carbohydrate. You can lose 4 or 5 pounds of weight in a few days, but most of it is water.
- When people are used to blood sugar highs and lows they take better control of their eating when they initially go low carb because their blood sugar stabilises and their hunger pangs improve. So, they also lose some weight in the early stages as they feel less hungry initially.
The last point sounds like it should allow you to continue losing weight for months at a time, but there’s another side to satiation. One problem with low carb is a lack of food volume. Bulky carbs, fruit and most vegetables are out on a low carb diet, so the stomach rarely gets to swell and feel full. This is an important element of satiation which is missing. People begin to miss that full feeling and see the return of hunger and cravings associated with fullness. That’s certainly how I felt. I needed to feel full, but feeling full on a high fat diet is a recipe for overconsumption of calories.
This is one reason why people plateau. Another is a loss of muscle and metabolism. Carbs tend to keep the metabolism stoked and when you take them away there’s a drop in whole body metabolism and NEAT (Non-exercise activity thermogenesis). People feel less energetic, they take every opportunity to sit, to lean against things, they fidget less and generally expend less energy. As you’ll see, it’s also my view that it’s difficult to hang on to muscle with a low carb approach, so there’s going to be a small metabolism drop due to lost muscle and less energy expended in the gym due to reduced energy levels and power output.
Why a low carb approach doesn’t stack up
The first thing to say is that weight loss is purely about energy balance. I’m using the word ‘weight’ deliberately here. If you consume fewer calories than you expend you will lose weight. This is so absolute, you could probably prove it from first principles using the first law of thermodynamics. Let’s not go there! Let’s just say it’s the one assertion upon which we can rely.
So, with that in mind, let’s do a quick thought experiment. Imagine an ordinary person with a calorie requirement of 2000 calories per day. You drip feed this person with 1g of carbohydrate every 4 minutes for 24 hours – that’s 360g carbs, 1440 calories. This means they are 560 calories short of their energy requirement for that day. Do this for a week and they will lose weight – around 1lb.
This theoretical person is receiving 1440 calories of carbohydrate but burning 2000. So where is the extra energy coming from that enables them burn 2000 calories per day? You might say that because they are constantly receiving carbohydrate then they must have insulin circulating constantly too and so lipolysis will be turned off, so they can’t be using fat as a fuel – they must be burning muscle protein (via muscle protein breakdown and gluconeogenesis), right? But insulin also inhibits muscle protein breakdown, so they can’t be burning protein either. If they’re not burning fat and they’re not burning muscle and they’re only receiving 1440 calories of carbohydrate, what fuel are they burning for the remaining 560 calories? From where in the body is the 1lb of lost weight coming?
The answer is … mostly fat. And here’s why. Insulin is not an on/off switch. Its presence does not switch off fat burning. It’s more of a dose-dependent suppression of lipolysis than a sudden cessation. Something like this:
At low levels of insulin some lipolysis still takes place. Only at high doses is lipolysis switched off. This is an important point, and one that’s worth a diversion from the thought experiment.
Back in the real world, quickly digested carbohydrate is going to switch off fat breakdown because it elicits a large and rapid release of insulin. Food wise, that generally means anything that is high on the Glycaemic Index – refined carbs, sugary carbs. This is one reason why you’ll hear repeatedly that you should cut down on sugar. The other reason is that refined carbs can lead to poor eating behaviours. After insulin has cleared the blood sugar you’re going to get a sugar-low – a period where your blood sugar levels are right down and triggering ravenous hunger and cravings. If you can resist the cravings then you’ll ultimately stabilise and resume lipolysis but that’s generally not what happens. Most people give in to the cravings, seek more refined instantly gratifying carbs and repeat the cycle. They end up overconsuming calories and switching off lipolysis almost round the clock.
There has been a tendency for all carbs to be tarred with the same brush as sugary carbs. This is a shame because slowly digesting, fibrous, unrefined carbs, in my view, are an important part of a good healthy balanced diet. The message should be ‘right carb, not low carb’.
Returning briefly to the thought experiment, be aware that lipolysis is a complex function that has many paths and different enzymatic catalysts. There is a certain level of basal lipolysis that is not influenced by insulin and so is unaffected. This also helps with some lipolysis in the presence of insulin.
Back in the real world again, there are other reasons why fat burning can take place with a higher carb diet:
- In the periods between meals, especially approaching the next meal, insulin is low, glucagon is high, lipolysis takes place readily.
- Eating slower digesting carbs will give rise to a moderate insulin response and allow some lipolysis.
- Exercise helps to keep you sensitive to insulin. That’s important. If you are sedentary your sensitivity to insulin will become impaired. That means your blood sugar will not be cleared as quickly and insulin will remain high for longer. The body keeps producing insulin for as long as the blood sugar is raised. If this continues to the next meal then you have a situation where lipolysis is switched off constantly. If you exercise you’re going to be efficient with blood sugar control and lipolysis will not be hampered by constantly high insulin levels.
- Exercise also negates the anti-lipolytic and lipogenic effects on insulin and gives rise to other beneficial fat burning hormones such as growth hormone and adrenaline.
- Do some cardio fasted first thing in the morning and you take advantage of low insulin, high glucagon, growth hormone, testosterone and cortisol. Throw some caffeine in and you get adrenaline too. You can burn lots of fat in this cardio session. It’s also a great way to upregulate the fat oxidation machinery – mitochondria, enzymes, transportation. That will make you good at oxidising fat and tend to make you preferentially burn fat at other times of the day. So, it helps you preserve other potential fuel sources – carbohydrate and muscle protein.
- Intermittent fasting may be a good way to maximise fat burning whilst on a higher carb diet. Avoid carbs – or even food altogether – for 12-16 hours a day, taking in the crucial morning period. Shovel in your carbs for the remaining 8 hours and take advantage of insulin’s muscle preserving properties.
That’s quite a number of points around how to continue to burn fat whilst on a higher carb diet, but it mainly boils down to two points
- Eat the right carbs.
It’s the same advice you’ll have heard many times before. One of the reasons you’ll have heard it many times before is because it’s also what The UK Government says. The Government recommends more than 50% of calories from carbohydrate. Take a look at page 6 and 7 of this report, for example. If you’re in any doubt about the scientific rigour behind government recommendations then take a look at some of their other publications. This one just talks about energy requirements and doesn’t begin to cover the topic of macronutrient splits. To me, knowing how much knowledge, experience and research has gone into the Government recommendations, it’s reassuring that my recommended approach is in line with The Scientific Advisory Committee on Nutrition.
So, in summary, if the rationale for going low carb is to avoid switching off lipolysis then it doesn’t hold water. There are lots of opportunities for fat breakdown on a high carb diet and, in addition, you reap the benefits of having more carbs in your food.
The benefits of carbs
So, having just stated there are benefits to having lots of carbs, let me talk you through some of them.
- Carbs are brain fuel! The brain is one of the only organs that cannot use fat as a fuel. It’s a carb lover. Take away carbs, as you would on a low carb diet, and the first thing that happens is you get brain fog. You experience a period of slow thought process and general stupidity while your brain adjusts to using ketones.
- Carbs make you happy – carbs trigger a reward response in the brain and the release of serotonin which contributes to feelings of well-being and happiness.
- Carbs are anabolic. That means they help you gain or preserve muscle. One of the main influences of muscle growth is the energy status of muscle cells. And what’s the main fuel of muscle cells? Carbohydrate. Take it away and you reduce the energy status of muscle cells and impair muscle growth.
- Insulin is net anabolic. Insulin prevents muscle protein breakdown. If you can stimulate some muscle protein synthesis and prevent breakdown then, net, you will be anabolic. Insulin also helps to shuffle carbohydrate and other nutrients into muscle cells, aiding with growth and repair.
- Carbs fuel workouts. When you train at high intensities, like you do when you are lifting weights, then the body uses carbohydrates as a fuel source almost entirely. You’ll find you lack energy if you deplete muscle carbohydrate stores by going low carb. The body can make carbohydrate via gluconeogenesis to keep fuelling a workout but the process is inefficient and can’t always cope with the demand. Worse still, the body uses muscle protein as a raw material for gluconeogenesis. Definitely not what you want! Make the most of your workouts, keep hold of your muscle and stay anabolic – carb up!
- Carbs provide fibre. Wholegrains, fruits, vegetables, pulses – all fantastic sources of fibre and all highly restricted on a low carb diet. Take them away and you risk, at best, constipation. But there is also an association between low fibre diets and cancer. Get your fibre, get your carbs.
What about diabetics?
Our experience with clients is that those who initially present with high blood sugar are able to get that down in to normal ranges within a month of starting the programme. Sounds dramatic, but it’s simply a question of making better food choices and restoring insulin sensitivity through a structured exercise programme.
So far, we haven’t had someone with full blown exhausted-pancreas type 2 diabetes. I doubt whether, for those people, simply improving the diet and doing some exercise would have the same effect. But for anyone who hasn’t reached that stage yet I see no reason to keep carbs down aside from possibly in the first month whilst they restore their blood sugar physiology.
Is there anything good about low carb diets?
Yes! There’s no doubt that blood sugar will experience more ups and downs when carbs are plentiful and regular, even if you make slow digesting choices. So, carbs may make you hungry, particularly if you make bad choices. If your issue is cravings or frequent hunger despite sufficient calorie intake, then you may do well on a low carb diet.
Having said that, I do think you should be able to avoid hunger. If you get plenty of fibre, lean protein and lots of veggies, you should be able to eat frequently and copiously without ever really feeling hungry.