How Low-Carb Diets Work

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How Low-Carb Diets Work

Low Carb Diet

With so many diet success stories, low-carb dieting has become very popular. How does low carb REALLY work? What is important to keep in mind when going low carb? Here’s what you need to know.


  • Low carb diets (< 50 g carbs per day) are effective for short-term weight loss because most people end up eating less calories.
  • Insulin does not make you fat. Equal weight loss happens with low fat diets as low carb diets when calories and protein are accounted for.
  • Prioritize polyunsaturated fat from plant sources if you go low-carb, otherwise you increase your risk of heart disease by 30%.
  • You can get the benefits of low carb diets without the risks by following our Diet Like a Doctor fat loss system.

How low-carb diet works

On a low carb diet you’ll eat less than 50 grams of carbohydrates per day. Thus you’ll limit high carb foods like classic sugary candy, chocolate, soda pop, cakes and pastries. Also off limits are rice, pasta, bread, cereal grains, flour, fruits, and even vegetables like beans, lentils, peas and potatoes. Some also limit dairy. This means you’ll likely eat less calories per day compared to you old diet, and that’s how low carb diets cause weight loss.
Eating less carbs will lower your hormone levels of insulin, but it’s a myth that this causes fat loss. A low carb low insulin diet causes the same amount of fat loss as a low fat high insulin diet when calories and protein intake are equal (1). The opposite is also true: adding fat has the same effect on fat balance as adding carbs, when calories are equal (2). Even a diet with only white rice, fruit, juice, and white sugar caused 140 pounds (64 kg) of weight loss (3). 

Low Carb Foods

How low-carb is keto?

Less than 20 grams of carbs per day is keto. This means that your body’s main fuel source is fat from your diet, and this fat is broken down into ketones to be used for energy. Thus more ketones can be detected in your blood and urine. This is called ketosis. If the food you eat doesn’t give your body enough calories, your body will start burning your stored fat as well just like with any other diet. Read our full article on keto here

Are low-carb diets good?

Low carb diets are good for short-term weight loss, BUT not for long-term health. Based on studies lasting between 12 weeks and 1 year, low carb diets help you lose weight because they make you eat more vegetables and protein, so you eat less calories (13). This weight loss can make some health markers improve too (12), but, because most low carb diets make you eat more animal products and saturated fat, long term studies show that they increase your risk of dying from heart disease by 30%. (14)

This is based on studies LONG-TERM studies lasting between 4 to 20 YEARS, from all around the world including Sweden, Greece and the US (15). If you want to go low carb safely, make sure you are getting most of your fats from fish, olive and rapeseed oils, seeds, nuts and avocados and less fat from butter, red meat, chicken and eggs. Read our full article on saturated fat here.

Low-carb diet to lose weight?

There is no guaranteed weight loss at any carb level, because it’s the calories that matter for weight loss. Most people will cut calories enough when eating less than 20 grams of carbs per day, but if you eat enough calories from butter, bacon and nuts, you will still gain weight, even if you are at 0 grams of carbs.

On low-carb diet and not losing weight?

This is because you are eating foods high in calories, even if they are low in carbs. If you are eating too many calories, your body will store fat even if you get your carbs and insulin levels to zero. In low carb diets, butter, salted roasted nuts, and high fat meats like bacon pack loads of calories and are easy to overeat, stopping you from losing fat. Try replacing these foods with low calorie spreads, unsalted nuts, and leaner meats and you’ll see better results. Also consider adding beans, lentils, boiled potatoes and fruit to your diet to keep you full without adding too many calories.

Research on over 132 000 people shows that calories matter more than how much carbs or fat your diet has (4). We haven’t found any study trying to make people gain weight on a zero-carb diet (probably for ethical reasons), but we found plenty of research showing that weight loss can happen with high and low carb diets (1-3).

On low carb-diet: what can I eat?

Low carb diets let you eat meat, chicken, fish, most vegetables, nuts, seeds, butters and oils. Vary your vegetables from cabbage, kale, cauliflower, broccoli, avocados, carrots, spinach and other leafy greens. While dairy isn’t allows, eggs are! Your meals will typically have a large protein source from beef, chicken, fish, or pork served with plenty of vegetables.

Can low-carb diet cause bloating?

Bloating is very individual and depends on what type of bacteria you have in your gut microbiome. Some feel low carb diets REDUCE bloating, but studies are few (5). Foods that are known to cause bloating are FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) (6). Avoid eliminating all FODMAPs on your own as you risk eating too little vitamins. Instead, talk to your doctor or dietician for a better approach.

Can low-carb diet cause joint pain?

Nobody knows for sure, because there’s no good research (7). But it certainly depends on WHY you have joint pain. Rat studies find low carb diets reduce inflammation related to gout, a joint disease where uric acid makes joint flare up (8).

Can low-carb diet make you tired?

Yes, especially if you work out a lot. This is because carbs fuel athletic performance, especially if you are doing pulse-raising exercises like running, swimming or sports. (9) Carbs are less important for fueling regular weight lifting exercise (10). Even if you don’t work out, the lower calorie intake will make you feel tired, moody and more irritable. This is common for ALL diets, and is related to the calories you eat, not the amount of carbs (11). 

What low-carb foods give you energy?

Low carb foods that pack energy (calories) are mostly nuts and seeds. The branched chain amino acids from meat can also help you feel less tired, but once again it’s the calories that will be the biggest decider of your energy levels (11). If you are feeling low on energy on a low carb diet, consider taking a diet break for at least a week, and also make sure your have you’re getting enough sleep, not working out too hard and make room for enough daily recovery after stressful activities.

How to succeed with low carb without the risks

If you are looking to lose fat and you are tired of fad diets, our eBook Diet Like a Doctor helps you stay lean. Each chapter provides practical steps to make changes NOW. Unlike other diet books, Diet Like a Doctor is completely evidence based with over 250 scientific references. Click here to learn more.


1. Hall et al 2017. Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition

2. McDevitt et al 2000. Macronutrient disposal during controlled overfeeding with glucose, fructose, sucrose, or fat in lean and obese women.

3. Kempner et al 1975. Treatment of massive obesity with rice/reduction diet program. An analysis of 106 patients with at least a 45-kg weight loss.

4. Anderson et al 2016: Adiposity among 132 479 UK biobank participants: contribution of sugar intake vs other nutrients

5. Goldstein et al 2000. Carbohydrate malabsorption and the effect of dietary restriction on symptoms of irritable bowel syndrome and functional bowel complaints.

6. Shepherd et al 2008. Dietary triggers of abdominal symptoms in patients with irritable bowel syndrome: randomized placebo-controlled evidence.

7. Masino et al 2013. J Child Neurol. Ketogenic diets and pain.

8. Goldberg 2017. Cell Rep. β-Hydroxybutyrate Deactivates Neutrophil NLRP3 Inflammasome to Relieve Gout Flares.

9. Kerksick et al 2018. ISSN exercise & sports nutrition review update: research & recommendations.

10. Escobar et al 2016 Br J Nutr. Carbohydrate intake and resistance-based exercise: are current recommendations reflective of actual need?

11. Karl et al 2015. Physiol Behav. Transient decrements in mood during energy deficit are independent of dietary protein-to-carbohydrate ratio.

12. Gardner et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial

13. Anderson et al 2016: Adiposity among 132 479 UK biobank participants: contribution of sugar intake vs other nutrients

14. Jeremiah Stamler, Diet-heart: a problematic revisit, The American Journal of Clinical Nutrition, Volume 91, Issue 3, March 2010, Pages 497–499

15. Noto et al. Low-Carbohydrate Diets and All-Cause Mortality: A Systematic Review and Meta-Analysis of Observational Studies.

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