Low-carbohydrate diets or carbohydrate-restricted diets (CRDs) are diets that restrict carbohydrate consumption. Foods high in carbohydrates (e.g., sugar, bread, pasta) are limited or replaced with foods containing a higher percentage of fats and moderate protein (e.g., meat, poultry, fish, shellfish, eggs, cheese, nuts, and seeds) and other foods low in carbohydrates (e.g., most salad vegetables such as spinach, kale, chard and collards), although other vegetables and fruits (especially berries) are often allowed.
Ketone bodies synthesized in the body can be easily utilized for energy production by heart, muscle tissue, and the kidneys. Ketone bodies also can cross the blood-brain barrier to provide an alternative source of energy to the brain. RBCs and the liver do not utilize ketones due to lack of mitochondria and enzyme diaphorase respectively. Ketone body production depends on several factors such as resting basal metabolic rate (BMR), body mass index (BMI), and body fat percentage. Ketone bodies produce more adenosine triphosphate in comparison to glucose, sometimes aptly called a "super fuel." One hundred grams of acetoacetate generates 9400 grams of ATP, and 100 g of beta-hydroxybutyrate yields 10,500 grams of ATP; whereas, 100 grams of glucose produces only 8,700 grams of ATP. This allows the body to maintain efficient fuel production even during a caloric deficit. Ketone bodies also decrease free radical damage and enhance antioxidant capacity.

Although the KD has shown promise as an alternative dietary strategy for weight management, it should be approached with caution. Acutely, the KD causes physiological changes which may manifest as the “keto flu,” a set of symptoms which commonly includes headache, nausea, gastrointestinal upset and fatigue. A recent study by Urbain et al. (22) illustrates this point, as they state, “Consistent with other studies, our subjects complained about headache, gastrointestinal symptoms, and general weakness mainly during the 1-week metabolic adaptation phase to a KD.” While these symptoms typically resolve within the first one to two weeks, this may present an unpleasant barrier for many individuals to overcome.
It’s also currently as trendy to the fitness world as kale and açaí are to the pseudo-hipsters who wear beanies, even in the dead-heat of summer. If you haven’t tried keto on for size, maybe give it a go (unless you’re a complete and utter carb bitch, and cramming yourself full of bagels and pancakes just makes your abs really pop - in which case, the rest of us hate you on the inside. Just a little.)
Dr. Josh Axe, DNM, DC, CNS, is a doctor of natural medicine, clinical nutritionist and author with a passion to help people get well using food as medicine. He’s the author of the books “Eat Dirt: Why Leaky Gut May Be the Root Cause of Your Health Problems,” “Essential Oils: Ancient Medicine” and the upcoming “Keto Diet: Your 30-Day Plan to Lose Weight, Balance Hormones, Boost Brain Health, and Reverse Disease” (February 2019, published by Little, Brown Spark). He’s a co-founder of Ancient Nutrition, a health company where the mission is to restore health, strength and vitality by providing history’s healthiest whole food nutrients to the modern world.
Sleep enough – for most people at least seven hours per night on average – and keep stress under control. Sleep deprivation and stress hormones raise blood sugar levels, slowing ketosis and weight loss a bit. Plus they might make it harder to stick to a keto diet, and resist temptations. So while handling sleep and stress will not get you into ketosis on it’s own, it’s still worth thinking about.

Many unhealthy foods easily meet keto’s low-carb, high-fat criteria. However, that doesn’t mean you can or should eat them freely. “A huge benefit to following the keto diet is that the vast majority of processed food is removed with the removal of grains,” Santo says. “Unfortunately, poor-quality dairy, meat, and veggies may fill the gap.” Look for healthier sources of protein and fat, such as grass-fed meats, and limit processed dairy (think cheese singles) as much as possible.
Sexual dysfunction in subjects with obesity has been scarcely studied. Recent studies evidenced a rate of sexual dysfunction in 29–60% of women and 24.8–45% of men with obesity [50]. In the current study, at baseline, the obese men reported a relatively good sexual function based on the EMAS–SFQ. The domains included in this questionnaire correlated with levels of testosterone, and the EMAS-SFQ scores reported in the current study are higher than those previously observed in patients with low levels of testosterone [27]. Accordingly, we did not find significant changes in the sexual function of men during the nutritional intervention. By contrast, women reported a general sexual dysfunction that improved, especially in the maximum ketosis phase, and then during the intervention. More concretely, women exhibited an improvement in excitation, lubrication, and orgasm capacity. Sexual dysfunction is usually related to impairments in parameters related to healthy, body image dissatisfaction, depressive symptoms, and lower levels of romantic relationship satisfaction [51]. Then, it could be hypothesized that the beneficial effects on several parameters of body composition and biochemicals induced by the VLCK diet, PNK method®, could be involved in an improvement in the sexual function of obese women.
But what does the science say? Results are mixed. In one Spanish study of 20 obese adults, participants were put on a low-calorie keto diet and lost an average of 40 pounds over four months. Another small experiment had a similar outcome. In a six-month Experimental & Clinical Cardiology study of 83 obese adults, those on the keto diet lost an average of 33 pounds, while lowering their bad (LDL) cholesterol levels and increasing their good (HDL) cholesterol.
Various mechanisms may explain the variations in body water. For example, glycogen depletion induced by VLCK diets could cause a marked increase in diuresis, given that glycogen is usually stored together with water (39, 40). Water loss might also be associated with ketonuria, because ketone bodies increase the renal sodium and water loss as a result (39, 41). These assumptions seem reasonable considering that the peak water loss coincides with the phase of maximum ketosis. However, the mechanisms explaining the diuresis observed with VLCK and with most hypocaloric diets are not known at present (30). Contrary to previous observations (42, 43), DXA analysis evidenced a maintenance in bone mineral density in the current study.
For obesity-reduction experts, it is well known that the main obstacle to follow a hypocaloric diet is hunger. In fact, within a few days after undertaking such a calorie-lowered diet, patients suffered a battery of negative effects, such as hunger, sadness, bad humor, and, in some cases, mild depression. All these side effects were absent in the patients following a VLCK diet, thus contributing to the success of these types of treatments. The mechanism that erases hunger and sadness in obese subjects following a VLCK diet are not known, and several authors strongly believe that it is due to the anorexigenic effect of ketosis [42]. As a result, of that rationale, the target of this work was to study the neurocognitive effects of ketosis, using a battery of neurocognitive and QoL tests in the same individuals at three different stages; (a) nonketosis-nonweight reduction (basal), (b) highly ketosis-mild weight reduction (visit 2), and (c) nonketosis-strong (mean 20 kg) weight reduction.
Ketosis was determined by measuring ketone bodies, specifically B-hydroxybutyrate (B-OHB), in capillary blood using a portable meter (GlucoMen LX Sensor, A. Menarini Diagnostics, Neuss, Germany) before measurements of anthropometric parameters. As with anthropometric assessments, all of the determinations of capillary ketonemia were made after an overnight fast of 8 to 10 hours. These measurements were performed daily by each patient during the entire VLCK diet, and the corresponding values were reviewed on the machine’s memory by the research team for managing adherence. Additionally, B-OHB levels were determined at each complete visit by the physician in charge of the patient. The measurements reported as “low value” (≤ 0.2 mmol/L) by the meter were assumed to be zero for purposes of statistical analyses.
The nutritional intervention was based on a commercial weight-loss program (PNK method®), as was described elsewhere [4]. Briefly, the intervention included an evaluation by the specialist physician conducting the study, an assessment by an expert dietician, and exercise recommendations. This method is based on high-biological-value protein preparations obtained from cow’s milk, soy, avian eggs, green peas, and cereals. Each protein preparation contained 15 g protein, 4 g carbohydrates, 3 g fat, and 50 mg docohexaenoic acid and provided 90–100 kcal.
Of the 28 participants enrolled in the study, 21 completed the 16 weeks of follow-up. Reasons for discontinuing the study included unable to adhere to study meetings and unable to adhere to the diet; no participant reported discontinuing as a result of adverse effects associated with the intervention. All but one of the 21 participants were men; 62% (n = 13) were Caucasian, 38% (n = 8) were African-American (Table ​(Table1).1). The mean age was 56.0 ± 7.9 years.

I personally don't follow a very low-carb diet because I have such a preexisting condition which may have been caused by my calorie-restricting dieting many years ago. My "ideal" level is somewhere around 30 grams of net carbs (light ketosis). By "ideal" I mean a level at which I feel great and maintain a healthy weight. I sometimes eat less carbs out of habit, not because I force myself to follow a very low-carb diet. Following a very low-carb diet (less than 20 grams of total carbs) doesn't help in my case: it made no difference to my appetite or energy levels but I felt worse. You simply need to try it yourself and find your "ideal" carb intake.
People claiming huge benefits of these supplements – despite the lack of solid scientific support – may sometimes have a financial reason to believe in the supplements. Some of these products are sold under a multi-level marketing arrangement, where sales people are paid based on commission. For example, the company Prüvit sells drinkable ketones, called KETO//OS with a multi-level marketing structure.
Low-carbohydrate diets are associated with increased mortality, and they can miss out on the health benefits afforded by high-quality carbohydrate such as is found in legumes including grain legumes or pulses, and fruit and vegetables.[3][4] Disadvantages of the diet might include halitosis, headache and constipation, and in general the potential adverse effects of the diet are under-researched, particularly for more serious possible risks such as for bone health and cancer incidence.[5]
Prior to the advent of exogenous insulin for the treatment of diabetes mellitus in the 1920's, the mainstay of therapy was dietary modification. Diet recommendations in that era were aimed at controlling glycemia (actually, glycosuria) and were dramatically different from current low-fat, high-carbohydrate dietary recommendations for patients with diabetes [1,2]. For example, the Dr. Elliot Joslin Diabetic Diet in 1923 consisted of "meats, poultry, game, fish, clear soups, gelatin, eggs, butter, olive oil, coffee, tea" and contained approximately 5% of energy from carbohydrates, 20% from protein, and 75% from fat [3]. A similar diet was advocated by Dr. Frederick Allen of the same era [4].
All anthropometric measurements were undertaken after an overnight fast (8 to 10 h), under resting conditions, in duplicate, and performed by well-trained health workers. Participants’ body weights were measured to the nearest 0.1 kg on the same calibrated electronic device (Seca 220 scale, Medical Resources, EPI Inc. (Lewis Center, OH, USA) in underwear and without shoes. BMI was calculated by dividing body weight in kilograms by the square of height in meters; BMI = weight (kg)/height2 (m).
In many developing countries, the ketogenic diet is expensive because dairy fats and meat are more expensive than grain, fruit and vegetables. The modified Atkins diet has been proposed as a lower-cost alternative for those countries; the slightly more expensive food bill can be offset by a reduction in pharmaceutical costs if the diet is successful. The modified Atkins diet is less complex to explain and prepare and requires less support from a dietitian.[55]
Dietary fiber keeps you full longer and contains prebiotic nutrients that support a healthy gut flora, creating a win-win for weight loss. Getting insufficient dietary fiber (yes, I'm talking to you, all-meat carnivore or cave-man diet folks) adversely shifts your healthy gut flora, which will increase inflammation, insulin resistance, fat deposition around the middle, and weight gain. Leafy green and cruciferous vegetables, avocado, coconut, and berries make great fiber-rich, keto-friendly foods.

Previous studies have shown that ketogenic diets preferably reduce the total FM in obese patients (10–13). However, the precise distribution of these losses has not been determined. In this study we confirmed that the diet reduces total FM and specifically visceral adipose tissue, which has a greater impact in predicting cardiometabolic complications associated with obesity than does the total volume of body adiposity (2, 31).

Before starting, ask yourself what is really realistic for you, Mattinson suggests. Then get your doctor’s okay. You may also work with a local registered dietitian nutritionist to limit potential nutrient deficiencies and talk about vitamin supplementation, as you won’t be eating whole grains, dairy, or fruit, and will eliminate many veggies. “A diet that eliminates entire food groups is a red flag to me. This isn’t something to take lightly or dive into headfirst with no medical supervision,” she says.
Similar to our results, three studies noted that diabetes medications were reduced in some participants[6,8,9], although details were provided in only one study. We also discontinued diuretic medications during diet initiation because of concern for additional diuresis incurred by the diet. This concern was based on the theoretical effects of the diet [17], observed effects of the diet on body water by bioelectric impedance [18], and practical experience with the diet [19]. Until we learn more about using low carbohydrate diets, medical monitoring for hypoglycemia, dehydration, and electrolyte abnormalities is imperative in patients taking diabetes or diuretic medications.
Much of the research into low-carbohydrate dieting has been of poor quality and studies which reported large effects have garnered disproportionate attention in comparison to those which are methodologically sound.[5] Higher quality studies tend to find no meaningful difference in outcome between low-fat and low-carbohydrate dieting.[5] Low-quality meta-analyses have tended to report favourably on the effect of low-carbohydrate diets: a systematic review found that 9 out of 10 meta-analyses with positive conclusions were affected by publication bias.[5]
Clinical improvement was observed in Alzheimer’s patients fed a ketogenic diet, and this was marked by improved mitochondrial function. (15) In fact, a European Journal of Clinical Nutrition study pointed to emerging data that suggested the therapeutic use of ketogenic diets for multiple neurological disorders beyond epilepsy and Alzheimer’s, including headaches, neurotrauma, Parkinson’s disease, sleep disorders, brain cancer, autism and multiple sclerosis. (16)
People use a ketogenic diet most often to lose weight, but it can help manage certain medical conditions, like epilepsy, too. It also may help people with heart disease, certain brain diseases, and even acne, but there needs to be more research in those areas. Talk with your doctor first to find out if it’s safe for you to try a ketogenic diet, especially if you have type 1 diabetes.
Long-term compliance is low and can be a big issue with a ketogenic diet, but this is the case with any lifestyle change.  Even though the ketogenic diet is significantly superior in the induction of weight loss in otherwise healthy patients with obesity and the induced weight loss is rapid, intense, and sustained until at least 2 year, the understanding of the clinical impacts, safety, tolerability, efficacy, duration of treatment, and prognosis after discontinuation of the diet is challenging and requires further studies to understand the disease-specific mechanisms.
Though technically a fruit, avocados offer a rich source of heart-healthy monounsaturated fatty acids (MUFAs). They're also packed with fiber to bolster digestive health. One-half of an avocado contains 161 calories, 2 grams (g) of protein, 15 g of fat, 9 g of total carbs, and 7 g of fiber (bringing it to 2 g of net carbs), notes the U.S. Department of Agriculture (USDA).
It’s estimated that over 50% of people are deficient in Vitamin D worldwide[*]. Although Vitamin D doesn’t play a major role in whether or not you are in ketosis, it is responsible for regulating immunity, inflammation, hormones and helping with electrolyte absorption[*][*] — all factors important for weight loss and overall health. Additionally, studies support the direct benefits of vitamin D for weight loss[*][*][*]. You can check your Vitamin D levels with a simple blood test and then supplement accordingly. When supplementing, choose Vitamin D3 as it is the form that’s best absorbed by your body[*][*].

Another concern for obese individuals is physical activity and sexual functioning. Relevantly, an increase in physical activity was observed during the intervention. This improvement agrees with the design of the nutritional intervention because the commercial weight-loss program (PNK method) includes lifestyle and behavioral modification support. All patients underwent a structured program of physical exercise with external supervision. According to these results, patients are encouraged to walk and to practice vigorous exercise.
In Asia, the normal diet includes rice and noodles as the main energy source, making their elimination difficult. Therefore, the MCT-oil form of the diet, which allows more carbohydrate, has proved useful. In India, religious beliefs commonly affect the diet: some patients are vegetarians, will not eat root vegetables or avoid beef. The Indian ketogenic diet is started without a fast due to cultural opposition towards fasting in children. The low-fat, high-carbohydrate nature of the normal Indian and Asian diet means that their ketogenic diets typically have a lower ketogenic ratio (1:1) than in America and Europe. However, they appear to be just as effective.[54]
The importance of dietary CHO is so well ingrained that the concept is taken for granted. In fact, basic macronutrient guidelines are predicated upon the idea that the central nervous system (CNS) requires a minimum of ~130 grams (~520 kcal) per day to function properly (i.e., to maintain optimal cognitive function). As a result, the minimum recommended daily intake of CHO reflects this idea (7). Similarly, most contemporary texts on sports nutrition emphasize the outsized role of CHO in optimizing both athletic performance and recovery (9). Frequently referred to as the “master fuel,” recommendations range from 3 – 12 grams per kilogram of bodyweight, per day. As an example, the recommended daily intake for a 180-lb athlete would be 246 – 982 grams, with a caloric equivalent of 984 – 3,928 calories. In marked contrast, the KD would recommend a maximum of just 50 grams (~ 200 calories) per day for the same individual.
In steps 4 or 5, the ketogenic phases were ended by the physician in charge of the patient based on the amount of weight lost, and the patient started a low-calorie diet (800–1500 kcal/day). At this point, the patients underwent a progressive incorporation of different food groups and participated in a program of alimentary re-education to guarantee the long-term maintenance of the weight loss. The maintenance diet consisted of an eating plan balanced in carbohydrates, protein, and fat. Depending on the individual, the calories consumed ranged between 1500 and 2000 kcal/day, and the target was to maintain the weight lost and promote a healthy lifestyle.
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