Are carbs fattening, or does it actually speed up your metabolism?
Carbs are very important when trying to lose weight. I have found that carbs provide superior satiety, compared to fats. Whereas when I eat too much protein at the expense of carbs, I completely lose my taste for protein, my energy feels low and I’m constantly craving carbs.
Can carbs actually speed up your metabolism?
Indeed so. Carbs increase leptin, which is a satiety hormone. A reduction in leptin levels, during weight loss, signals the brain to increase feeding and decrease energy expenditure, thyroid, androgen synthesis and immunity. (1) Many overweight and obese individuals actually have high levels of circulating leptin, but their leptin receptors are insensitive to it, hence, the body senses low levels of leptin. Calorie restriction and intermittent fasting are two easy ways to increase leptin sensitivity. Individuals who are more leptin sensitive are more successful in reducing their fat.
Furthermore, carbs provide energy for the muscles which enable you to get good workouts. This will also help you do the necessary volume, at the required intensity, in order to stimulate that anabolic response to help maintain your muscle mass during the cut.
The carb-induced insulin response is anti-catabolic on its own (even without any amino acids). It also increases the anabolic response to protein. Insulin is needed to drive amino acids into the muscle, and when the body is insulin resistant, muscle protein synthesis will be blunted. Low carb intake during dieting leads to lowered insulin and IGF-1, which makes it harder for the body to retain hard earned muscle. Maintaining exercise performance, due to greater glycogen availability, and the anti-catabolic effect of insulin, enables the body to retain more muscle mass. Even more so than testosterone levels. Meaning that, increased carb intake at the expense of fats (which increase androgen synthesis) is still better for retaining muscle, than having a little higher testosterone, but with lower carbs. (2)
Won’t carbs/insulin make you store more fat?
When liver glycogen is lowered after a fast, or muscle and liver glycogen is depleted after a workout, reloading on carbs will first be used to replenish those glycogen stores. Your liver is able to store about 100g and your muscles about 400g+. So let’s say you’ve depleted your liver glycogen and 200g of your muscle glycogen as well. Now you can easily load 300g of carbs back into your system, replenish your glycogen stores and nothing will be stored as fat. Insulin also increases glucose oxidation, so if there are any carbs left, it will be burnt up at a faster rate. For example: if you burn 10g of carbs per hour on an empty stomach, you’ll burn 12g+ of carbs an hour under the effect of insulin. This effect helps to prevent excess carb storage. Neither fat nor protein has this effect.
Eating more than 300g of carbs a day, during a cut, is a bit unlikely anyway. But let’s say you eat 400g of carbs, 100g will remain in your system. Firstly, insulin speeds up glucose oxidation and the enzyme that converts carbs to fats, fatty acid synthase/de novo lipogenesis (DNL), only converts a very small amount of carbs to fat during the day. However, under spontaneous feeding conditions, isotopic measurements of
de novo lipogenesis show that only 2 – 4% of glucose carbon atoms are converted into fatty acids. With a high carbohydrate diet, hepatic DNL does not exceed 5 – 10 g fatty acids synthesized per day, which is really low and would definitely not lead to fat gains.
DNL is also increased a bit more with fructose consumption, but only if the amount of fructose exceeds liver glycogen stores (100g<). But the cool thing about fructose is that it increases the enzyme pyruvate dehydrogenase, which transforms pyruvate into acetyl-CoA by a process called pyruvate decarboxylation. Acetyl-CoA will then be used in the citric acid cycle to carry out cellular respiration and produce energy. So fructose can be fattening when majorly overdone, but it actually speeds up energy production.
In this study by Hall et al. (4) compared two groups, one reduced carbs and the other reduced fats, while keeping protein intake the same. The reduced fat group actually got better fat loss than the reduced carbs. At the end of the study, insulin decreased significantly in the low carb group and remained the same in the low fat group, however this did not prevent fat loss. We can definitely reject the statement that carbohydrate restriction, and insulin reduction, is required for fat loss.
What about a ketogenic / low carb diet?
I have found that, on a ketogenic diet, your muscles will smooth out, you will lose your vascularity and size. After a refeed, you regain some size and vascularity again, but then it quickly goes away over the next few days. Apart from that, I experienced being really hungry all the time, moody, had bad sleep, adrenaline responses at night and a bunch more stuff, so it wasn’t fun at all. I find it much easier to diet when consuming carbs, as it provides superior satiety for me, gives me energy, picks up my mood, etc. I also feel I lose fat faster when I eat lots of carbs, instead of doing a keto diet. I have written an article about the research that low carb eating is better for losing fat and retaining muscle, but no study so far has been done on the athletic population who want to get really lean, below 10% body fat, and stay that way. So there isn’t a definite answer to if it’s better or not, but I find that this will differ from person to person.
A meta-analysis found, that when protein intake was equal in both groups, the high carb group actually had higher energy expenditure and fat loss than the low carb (ketogenic) group. Both energy expenditure (EE) and fat loss were slightly greater in the higher-CHO/lower-fat conditions by EE by 26 kcal/day for EE and by 16 g/d for fat loss. However, the authors conceded that these differences were too small to be considered practically meaningful. (3)
Research points out that carbs are very necessary to maintain exercise performance, and exercise is crucial for the anabolic stimulus to increase muscle mass, and also maintain it while dieting. Also, getting really lean on a ketogenic diet will really hammer your metabolism and hormonal profile, due to being so carb depleted for such a long time.
How much carbs should you eat?
To diet in order to get lean successfully, you must eat in a caloric deficit, exercise for the anabolic stimulus, and eat enough protein (more or less 1 gram per pound of bodyweight). When those are in order, I advise to eat enough fats to support good hormonal production, of about 10-30% of your calories, and then the rest of your calories can come from carbs. Don’t try to go too low on fats, as fats slow down intestinal transit and provide longer satiety when combined with carbs.
What kind of carbs are best to eat?
First off, it’s very important not to eat foods that can irritate your gut, which will then cause bad reactions in your body. Most people don’t even know they are eating gut-irritating foods. I advise to eliminate one potential food source for 1 week, and then reintroduce it into your diet, to see how you react to it. If you don’t react badly, keep it in your diet. If you react badly, it’s best to eliminate it from your diet.
Secondly, it would be best to eat wholesome, healthy, natural foods which are dense in nutrients. But, if you don’t like the food, but you think you have to eat it to get ripped, don’t eat it. However I highly advise to eliminate junk food and focus on healthy foods only, but for compliance reasons, alternatives can be consumed. Fruit (fructose) are great for replenishing liver glycogen, whereas glucose is superior for filling up muscle glycogen. So it can be a good idea to get the majority of your post-workout carbs from rice, potato, legumes, etc, and only a serving or 2 of fruit with it if you like. Bottom line is to eat healthy foods that you enjoy. Listen to your body, it knows what it needs (I’m not talking about junk food here).
Simple as that. Don’t overthink your diet and don’t think about food all the time. The secret to fat loss is to make it as effortless and enjoyable as possible. Carbs will help you do that.