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Carbohydrates: How Low Can You Go?

Like it or not, rapid fat loss is what prompts most clients to pay the large hourly fees charged by elite trainers. Regardless of his or her ability to improve core stability, deal with injuries, or establish rapport with a client, the majority of people will judge the value of a trainer on one thing: how much fat they strip off clients and how quickly they do it. In achieving this, intake of carbohydrates remains one of the most important factors and one of the most emotive.

The food industry-sponsored recommendations from the UK's Food Standards Agency suggest that individuals consume 60% of their calories from carbohydrates. Based on the allocated energy intake, this works out at a whopping 400g (14oz) per day for the average male and 320g (11oz) for females. Throughout the course of evolution, humans had no pasta, no bread and certainly no ice cream. Early men instead consumed less than half the carbohydrates than his successors do (Cordain, 2005).

It is therefore no surprise that a number of advantages exist in restricting carbohydrate intake compared to conventional recommendations. Excessive carbohydrate consumption has been linked with a wide range of health problems, from cardiovascular problems and type II diabetes to impaired neural function and suppressed immune system activity (Sanchez, 1973). Equally, low-carbohydrate diets can compromise output of thyroid hormones (Spaulding, 1976). Clearly, individuals want to find a level of carbohydrate intake that will support optimum health, maximize fat burning, and represent a sustainable and realistic dietary protocol.

Carbohydrate Metabolism: An Overview

Unlike proteins and fats, which the body uses for both energy and metabolic purposes such the production of hormones and cell membranes, carbohydrates are only used for energy. Thus, intake should reflect expenditure through physical activity. When your clients eat complex carbohydrates, for example wholemeal bread or brown rice, the starch contained within these foods is broken down by digestive enzymes collectively known as amylase. With amylase present in saliva, this process begins in the mouth but is primarily conducted in the small intestines. This amylase breaks down starches into simple sugars, which can then cross the intestinal barrier and increase the concentration of sugars in the bloodstream. If this process occurs too quickly – for example after the consumption of sugary foods, which can enter bloodstream in their existing state, or after eating refined carbohydrates in the form of white bread – then blood sugar levels rise excessively. Equally, a large amount of of carbohydrates in one meal can result in a huge rise in blood sugar levels.

Not only does this sharp rise in blood sugar cause problems, so, too, do the hormonal changes that follow. The increased sugars in the bloodstream can result in cardiovascular damage (Kapolsky, 2002), while the insulin released to counter it can increase aging and cause inflammation by releasing arachidonic acid from cell membranes (Fernandez-Real et al., 2003). While your clients might not be prompted to cut back on the spaghetti with these negative effects alone, they might find added motivation when they consider how effective carbohydrates are at fattening us up. High blood sugar levels and high insulin levels inhibit the oxidation of fat at mitochondria around the body and inhibit the breakdown and release of stored triglycerides at fat cells under the skin (Holt et al., 1997). In short, too many carbohydrates make people unhealthy and fat.

Low-Carb Diets

This realization prompted a wave of low-carbohydrate diets (notably The Zone, The South Beach Diet and The Atkins Diet) that capitalized on the public's hunger for such options. The rationale behind each diet varies slightly and the level of carbohydrates suggested varies significantly, but each aims to increase fat loss through the lowered insulin response that occurs when individuals cut back on the carbs. And with good reason: low carbohydrate (higher protein/fat) diets have consistently been shown to result in much more fat loss than their "conventional" equivalents (Shai, 2008). 

It is noteworthy that not every trial has shared the same conclusion; Harris et al. (1995) tracked weight loss in volunteers for 18 months and, although they only measured the body mass index of the cohort, they established a link between weight loss and dietary fat intake but not carbohydrate intake. This perhaps shows that there is more than one way to illicit weight loss, and that professionals should interest themselves not in “what works,” but “what is most efficient.” Different protocols may work more effectively for different people.

Keeping this in mind, the question is not so much whether or not low-carbohydrate diets are effective as how low should one go. In this regard, the choice is very much between a moderately-low carbohydrate diet – which I would define as one of between 100-150g (3-5oz) per day – and a very low carbohydrate (ketogenic) diet, where daily carb intake falls short of 100g (3oz).

The Ketogenetic Diet: An Altered Metabolic State

A ketogenic diet is one where the body enters ketosis. This is an altered metabolic state when, starved of carbohydrates, the body begins to use ketones as a fuel source. Ketosis begins to occur when carbohydrate intake drops below 100 grams per day and is defined as the concentration of ketones above 0.2 mmol/dl, with ketoacidosis defined at 7mmol/dl (Robinson, 1980).  Ketogenesis has faced severe criticisms for the potential to increase acidity in the bloodstream and, as a result, impair biological function and health. Concerns have also been voiced as to the amount of muscle breakdown that can occur during ketosis. Indeed, this is a valid concern as a ketogenic diet is catabolic by definition, making the building/rebuilding of muscle impossible The low level of carb intake can compromise muscle mass in the early phases. And, while endurance improves at lower intensities, performance of intense exercise suffers on a ketogenic diet (Hargreaves et al., 1995). Depending on food choices, the reduced consumption of carbohydrates may result in insufficient fiber intake and a negative impact on the composition of the intestinal bacteria and therefore colon health (Russell et al., 2011). These negative consequences should be taken into consideration whenever discussing a low-carbohydrate diet.

Regardless, fiber intake can be maintained by including vegetables like broccoli, cauliflower, spinach and green beans. All of these items provide fibrous bulk with only minimal carbohydrate content. Additionally, the evidence suggests that, in non-diabetics, restricting carbohydrates to induce dietary ketosis only briefly increases the acidity of the bloodstream and that this returns to normal after several days and that health can be maintained for long periods of ketosis (Withrow, 1980). It also reveals that such a restriction does increase protein breakdown from skeletal muscle for around three to four days, although the metabolic shifts that occur from this point onwards tilt the body into sparing protein, instead using fatty acids and ketones. This results in significant weight loss. A study of 120 overweight volunteers on a weight loss diet found that, after 24 weeks, those on the ketogenic diet lost twice as much fat mass as those on a low-fat diet (Yancy et al., 2004). Another study from the same year (Stern et al) followed volunteers one year after embarking on either a ketogenic diet or a "conventional" diet. Despite being matched for calorific intake, the first group had lost 5.1kg (11.2lb) to the 3.1kg (6.8lb) recorded by their counterparts.

In regards to health biomarkers, there is no consistent difference between moderately-low carbohydrate diets and that required to induce ketosis. There is also no doubt that ketogenic diets burn fat, and a lot of it. In this regard, ketogenic diets are not guilty of the charges levied at them by critics. A more relevant question is whether ketogenic diets burn more fat than moderately-low carbohydrate equivalents. Put another way, whether the fat-burning benefits of ketogenesis can be retained without the metabolic compromise that comes with it.

Ketogenic and Low-Carb Diets: The Evidence

Ketogenic diets certainly increase the rate of fat usage considerably, using free fatty acids / ketones for up to 90% of the energy used (Elia et al., 1990). However, the impressive use of fat may be offset by metabolic adaptations during reduced food intake. Researchers measured the drops in basal metabolic rate at an average of 26% after five days of starvation (Fuglei and Oritsland, 1999). Critics of the ketogenic diet point out that a starvation response does not occur in moderately-low carbohydrate diets. Most interesting is the research by Johnston et al. (2006), which split volunteers into two groups to directly compare a moderately-low carbohydrate diet against a ketogenic one. They fed both 1,500 kcals per day but providing the first with 157g (5.5oz) of carbohydrates per day and the other with 33g (1oz). The first group lost an average of 7.2kg (16lb), of which 5.5kg (12lb) came from fat; the ketogenic group lost 6.3kg (14lb), of which only 3.4kg (7.5lb) was from fat mass. This study suggests that a moderately low intake of carbohydrates appears more effective to improve body composition. Researchers also reported better mood in the moderately-low carbohydrate group. It should be pointed out that this study cannot conclude the issue (as the compliance of the volunteers may have affected the results) but it certainly strikes a blow in favor of the more moderate approach.

Using Low-Carb Diets

Charles Poliquin , one of the world's most respected strength coaches, remains an advocate for a low-carbohydrate diet and notes that athletes can still perform at a world-class level without gobbling down large quantities of pasta. However, he also believes ketosis is overrated and not necessary for making progress. Mauro Di Pasqaule, the author of The Metabolic Diet, suggests that five days of limiting carbohydrates to 30g (1oz) per day, following by two days of unlimited carbohydrate intake serves clients best to maximize both fat loss and muscle gains through a cyclical ketogenic diet; the aim is to put individuals into ketosis during the week but replenishes muscle and liver glycogen during the carb-up days, allowing both fat-burning and muscle growth over course of a full week. Dr. Loren Cordain points out that humans have evolved on a diet of 22-40% carbohydrate, which equate to 117-213g (4.1-7.5oz) per day for a client consuming 2,000 kcals. Importantly, these carbohydrates would have come exclusively from vegetables, nuts and (seasonally) fruit. It is also noteworthy that comparisons of paleolithic intake to modern times cannot be made directly, as our prehistoric ancestors were likely more active and consumed a higher amount of energy overall to fuel this.

Even so, I feel that this evolutionary diet falls right in the sweet spot that provides the right balance of insulin against glucagon and growth hormone, while representing a sustainable diet that can easily be maintained by clients in almost all situations. 

Naturally, the exact carbohydrate intake will vary from one person to the next; factors like lean mass, daily energy expenditure and precise aims will all make a difference. For exact calculations, a visit to a nutritional therapist experienced in this area is advised. For clients who are active only 1-2x per week and looking for weight loss, I would suggest food intake consisting of regular meals that feature plenty of meat, eggs and fish, combined with abundant vegetables and some large salads. This ”sweet spot” for these individuals would most likely be found when they follow the above guidelines and, additionally, get one or two servings of oats or brown rice alongside this over the course of the day. I would encourage clients to take an evening off from this once per week; not only can this help compliance and morale, but the occasional “re-feed” can help to avoid adaptations in energy efficiency and maintain a higher metabolic rate in the long-term (Ahima et al., 2000).

Together with the usual attention paid to stress, sleep, digestion and hydration, this represents an effective and reliable method of dropping fat mass quickly. Of course, it is not the only method and there is still no agreement on what constitutes the optimum intake of carbohydrates for weight loss. The fear some harbor against ketogenic diets appears unsubstantiated, although this more extreme approach may not offer any more spectacular results. They do, however, remain a useful tool. In any case, an examination of both the aims and the energy requirements of your clients should allow for consistent and impressive results. And a higher hourly rate.


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