Do low carb diets work?

In the 90s, low carb diets were very fashionable due to the release of The Atkins Diet book. Dr Atkins claimed that eating few or no carbohydrates was more beneficial for fat loss than a straight calorie deficit. Some of the studies are very out-dated and new research has showed conflicting evidence. The studies done back then were heavily manipulated in the favour of Dr Atkins to produce the results that he wanted. I am addressing this topic because this particular diet is becoming more popular recently under the name of the KETO (Ketogenic) DIET.



Before I get into the science, I am going to put it simply. Do low carb diets work? (assuming one is trying to LOSE weight/bodydfat)

YES if you are in a caloric deficit.
NO if you are at caloric maintenance/surplus.

So if you are in a caloric deficit- is there any need for a low carb diet at all? NO. You can and will lose weight by eating less calories than you use, period. But is there any advantage to eating low carbs? This question is not so simple and we will need to take at a few factors...

INSULIN SENSITIVITY

If you have good insulin sensitivity, you will handle dietary carbohydrates with ease. This is the case for most of the population. If you are towards insulin resistant, you will not respond very well at all. Or you may be completely resistant. This is known as typeII diabetes.
                It all depends on what your body's blood glucose levels are. Blood glucose goes down with age, so this is something you need to take into consideration, the older you are the less carbs you need and the more protein you need (due to decreased amino acid sensitivity which I will not go into!). Another factor is bodyfat %- a person with low bodyfat will be very sensitive to insulin and conversely, an overweight person will be more towards insulin resistant. The main factor that will affect insulin sensitivity is EXERCISE. All exercise, but more so resistance training is extremely beneficial to one's blood glucose levels (this is why you can get overweight people that exercise regularly that have excellent blood glucose levels). The last one is genetics- some people are born with good or bad sensitivity and there is little that can be done about it.

DO YOU HAVE GOOD INSULIN SENSITIVITY?

The only sure way is to get it tested, but that isn't going to happen as it is impractical so this is one way of doing it. Eat a large meal full of carbohydrates. 100g+ of whatever you like, pasta, potatoes, rice, sugar. Someone with good insulin sensitivity will have more energy after consumption and someone with not so good insulin sensitivity will fell tired and sluggish.

You may already know how you react, so keep this in mind and I will come back to it in a moment.

LOW CARB vs MED/HIGH CARB FOR FAT LOSS

see ref (3). Study shows insulin sensitive women on the high carb diet lost nearly double the weight as insulin sensitive women on the low-carb diet. Similarly, insulin resistant women lost twice the weight on the low-carb diet as on the high carb diet. Research conclusively shows that if you have good insulin sensitivity and low insulin secretion, odds are you will do well with a traditional bodybuilding type of diet which means high protein, highish carbs and low fat. If you’re not insulin sensitive and/or have high insulin secretion, a diet lower in carbs and higher in fat would certainly be more beneficial.

PUTTING IT ALL TOGETHER

If you still don't know whether you are insulin sensitive or not- try going on a very low carb diet for a week. You will enter ketosis (see ref 5 for more info). You may feel sluggish, tired and have what is known as 'brain fog' which is where you cannot think clearly and feel slow. If this is the case, you most likely have good insulin sensitivity and should go on a higher carb diet. If you feel fine, then you are not insulin sensitive and feel free to carry on and reap the rewards! 

So there you have it. Should you go on a low carb/KETO diet? If you are more towards insulin resistant then YES, but if you are insulin sensitive then NO. 

Thanks for reading, any questions please ask.
Tom

References:

1. Blundell JE, Cooling J. High-fat and low-fat (behavioural) phenotypes: biology or environment? Proc Nutr Soc. 1999 Nov;58(4):773-7.
2. Pittas AG, Roberts SB. Dietary composition and weight loss: can we individualize dietary prescriptions according to insulin sensitivity or secretion status? Nutr Rev. 2006 Oct;64(10 Pt 1):435-48. Review.
3. Cornier MA et. al. Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women. Obes Res. 2005 Apr;13(4):703-9.
4. Pittas AG et. al. A low-glycemic load diet facilitates greater weight loss in overweight adults with high insulin secretion but not in overweight adults with low insulin secretion in the CALERIE Trial. Diabetes Care. 2005 Dec;28(12):2939-41
5. http://en.wikipedia.org/wiki/Ketosis
6. http://www.bodyrecomposition.com/fat-loss/insulin-sensitivity-and-fat-loss.html