Ketogenic Diets: What You Need to Know

Ketogenic diets (Keto) have dominated the "popular” diet scene for the past two years, with no close contenders. Prior to Keto’s steady upsurge the popular-diet crown had long rested on gluten-free, although Paleo almost matched it for a few years.

Looking further back (except for the ‘low-fat’ 1990’s) a variety of low-carbohydrate/high-protein diets (i.e., Atkin’s, The Zone, South Beach, etc.) have generally topped the public’s interest. One should at least wonder, if any of these diets really worked then why do they lose popularity only to be replaced by another? 

So Considering Keto...

First of all, what is ketosis? Your brain and central nervous system function on only two fuels, glucose or ketones. Normally ketones would only come into play if you were literally starving—when carbohydrate intake is too low to provide enough fuel in the form of glucose. At that point your body shifts to converting the fuel it always has an abundance of (body fat) to ketones. Similarly, by limiting carbohydrate intake to just around 5% of energy intake (~20 to 50 grams per day) ketogenic diets trigger your body to shift into ketosis.

What is the theory behind ketogenic weight loss diets? Advocates of Keto assert that it's a path to easy weight loss due to to the following: First, because your body is utilizing fat as its main energy source that weight loss is faster. Second is the assertion that Keto has a “metabolic advantage” in the form of a bumped up metabolic rate. And the final assertion is better appetite regulation (you simply won’t be hungry) which makes lower calorie intake easier.

So how do these claims hold up? Ketogenic diets do shift energy metabolism to a predominantly fat-burning mode, but does this speed up weight loss? No, it does not. And actually there is no theoretical reason why it would speed weight loss because it does nothing that changes overall energy balance. We’d have to reconsider the laws of thermodynamics for that to be the case. Let’s look at two key studies.

The following two studies were both tightly controlled metabolic ward studies where every gram of energy intake and output (including urine and feces) were accounted for along with changes in body weight and composition (fat mass, lean body mass and water).

First is a classic nitrogen-balance study[1] comparing an 800-calorie ketogenic diet with an 800-calorie balanced diet both diets led to the same amount of body-fat loss and body-weight loss over the 50-day study. The ketogenic diet however, gave the appearance of more rapid weight loss in the beginning due to extra water losses: 61% versus 37% of early scale loss was water on the ketogenic and balanced diets respectively. Both diets contained the same amount of protein (50-grams) so they differed only in fat and carbohydrate.

More recently, an abbreviated version of this type of study was done by the National Institutes of Health comparing high-fat and high-carbohydrate diets.[2] Over the 6-day metabolic ward study the high-fat diet led to less fat loss than the high-carbohydrate diet (245±21-grams versus 463±37-grams respectively). Why the big difference, and why more fat loss on the high-carbohydrate diet? Because in the early stages of carbohydrate restriction the body breaks down and oxidizes protein (muscle) to maintain blood glucose levels. So in the short-term, the high-fat diet leads to greater muscle, glycogen, and water losses (creating the illusion of faster weight loss) than an equal-calorie high-carbohydrate diet. This well-known protein-sparing effect of carbohydrate is why medically-supervised very-low-calorie (liquid) diets are relatively high-carbohydrate/low-fat formulations.

The first two assertions of Keto advocates (an advantage to a higher rate of fat-burning and a general metabolic advantage) are shown to be false in these meticulous studies, and there are no competing metabolic ward studies that show otherwise.

Scores of studies over the past 40- to 50-years have compared various diets, and report a variety of results (mainly because they are too short or poorly designed, and sometimes outright bias). What is consistent however, is that whenever calories are held constant between two different diets, there is never a significant difference in weight loss. At this point it is exceedingly clear that any diet that creates an energy deficit leads to weight loss.[3]^,[4]

The Real world: People obviously don’t live in metabolic wards. In so-called "free-living" conditions, high protein diets consistently show greater weight loss at three months, and at six months. At one year however, the differences are no longer statistically significant. Why? First, both Keto and high-protein diets lead to excess loss of body water (for the first week or so). More importantly for the long term, the improved satiety effects of higher protein intakes lead to lower energy intake and therefor greater weight loss than a balanced or low-fat diet. Keto diets are only moderate in protein, but ketones have a strong satiety effect of their own[5]^,[6] which will certainly enhance the likelihood of maintaining a lowered energy intake. On the other hand, sticking to a ketogenic diet is especially challenging due to the severe level of carbohydrate restriction (5% of intake versus 40- to 55% of typical diet patterns).

The Bottom Line: of the three proposed advantages of keto diets only reduced appetite is a supportable claim. Given the laws of thermodynamics there is no theoretical reason why changes in fuel oxidation (increased fat-burning) would enhance weight loss. The same goes for the notion of “metabolic advantage” (which also fails to materialize in calorie-controlled studies).

Other important considerations: the long-term health effects of Keto remain to be determined.^[7] Specific areas of concern include a negative impact on the microbiome (resulting in leaky gut, and autoimmune response and systemic inflammation^[8]), reduced micronutrient intakes, enhanced loss of lean body mass, increased homocysteine levels, increased LDL-cholesterol and reduced bone mineral density via excess calcium excretion.[9]

Final thoughts: If you want success with your weight and health the tried and true approach is to learn how to eat in a healthy way and in healthy amounts. My best advise is to start where you are at, and look for "easy changes" to improve the quality of your diet. Forget "going-on-a-diet," instead approach it as a lifestyle change. It would also help a lot to understand more about how your body works. Here are some links that can help you get started:

• The Game of Weight Loss has Rules
• 5 Things You Need to Know about Protein for Healthy Weight Loss
• Manage Yourself to Success!

All the Best!
-Dorene

PS--you might also be interested in: Can You Spot a Sham Weight Loss Diet? 

References:

---

[1] Yang and Van Itallie: Composition of Weight Lost during Short-Term Weight Reduction: Metabolic responses of obese subjects to starvation and low-calorie ketogenic and nonketogenic diets. J Clin Invest 1976;58:722-730.

[2] Hall K, et al.: Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity. Cell Metabolism 2015;22:427-436.

[3] Obert J, et al.: Popular Weight Loss Strategies: a Review of Four Weight Loss Techniques. Curr Gastroenterol Rep 2017;19(12):61.

[4] Atallah R, et al.: Long-term effects of 4 popular diets on weight loss and cardiovascular risk factors: a systematic review of randomized controlled trials. 2014;7(6):815-827.

[5] Gibson aa, et al.: Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obes Reviews 2015;16:64-76.

[6] Johnstone AM, et al.: Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum. Am J Clin Nutr 2008;87(1):44-45.

[7] Hamdy O, et al.: Fat Versus Carbohydrate-Based Energy-Restricted Diets for Weight Loss in Patients with Type 2 Diabetes. Curr Diab Rep 2018;1812(128).

[8] Tambo A, et al.: The Microbial Hypothesis-Contributions of Adenovirus and Metabolic Endotoxaemia to the Pathogenesis of Obesity. Intl J Chron Disease 2016;7030795.

[9] Adam-Perrot A, et al.: Low-carbohydrate diets: nutritional and physiological aspects. Obes Rev 2006;7(1):49-58.

CLAIM #4: Drinking Water Boosts Your Metabolism

This is entry #4 in a 9-part series on Metabolic Myths.

Metabolism-boosting hype generally has a grain of truth behind it that has been way overblown. In other cases, long disproved theories continue to be touted because they are super effective as click-bait (or selling books). You rarely see any actual numbers -- how many calories per day will this raise my resting metabolic rate? -- attached to claims. That’s because for the most part the actual increase (if any) in resting metabolic rate (or other components of your daily total energy expenditure), is too small to be of any practical significance.

Metabolism mythology has a life of its own though as it gets regurgitated and reposted throughout the internet and fad-diet books (and unfortunately even by many otherwise reputable sources).

Review "Metabolism" here: Metabolic Rate

My last topics were eating more frequently, muscle and breakfast, today's topic is water:

CLAIM: drinking water (or especially cold water) increases your metabolic rate.

Three semi-recent studies reported that drinking cold water increased metabolic rate by 24- to 30%.i ii iii These studies involved 500-ml (16.9-oz.) of cold water, and the increase in metabolic rate after drinking lasted about 60 minutes.

The author of one of these papersⁱⁱ concluded that, drinking 2 liters (67-oz.) of water per day would augment resting energy expenditure (REE) by approximately 95-calories.

Stunned by these extraordinary results (compared to data from previous studies), several researchers set up their own new studies. Brown (2006)iv found that cold water increased REE by only about 5%, while room temperature water had no effect. Girona (2014)v tested the metabolic response to drinking cold, room temperature, and body-temperature water. Cold and room temperature water increased REE by 2.9% and 2.3% over 90 mins. And most recently, Charriere (2015)vi tested drinking (room temperature) water against “sham drinking” (raising a glass of water to the lips pretending to drink, but not drinking). The water drinking led to a marginal (2.7%) increase in REE, but the result was not a statistically significant difference from the response to sham drinking (1.5%).

In summary, the vast majority of studies have found a tiny (if any) increase in REE from water drinking (0- to <5%).iv vi vii Furthermore, the non-significant differences found between drinking cold, or room-temperature water, and “sham-drinking” (pretending to drink the glass of water), calls into question whether water-drinking itself is actually even the variable affecting REE.vi

Just for fun, let's shift to considering the tiny bump in REE that some studies showed. What is the most that bump in REE could add up to?

For 40-year-old, 166-lb. female with an average REE (1,421-kcals) a 5% increase in REE (that lasts for 60-minutes), adds up to just 1.75-calories.

Remember this is for drinking 500 ml (16.9-oz.) of water. For 2 liters of water the bump would add up to 7-calories, which is equivalent to a scant half-teaspoon of sugar.

So while technically it might be argued that drinking water can increase REE, in fact—once again—we have a metabolic myth that has no practical significance.

In closing it's important to note that there's absolutely nothing that's healthier for you to drink, than water. As I've written about before (Is what you're drinking helping...), most people don't drink enough water, and should choose their beverages more carefully.

If you read this far and wondered why I didn't touch on the purported "fat-burning" effects of water it's just because this blog is already too long! I have it on my calendar for 2018 though, so check back from time to time.

All the Best!
Dorene

Related articles:
Is what you're drinking helping or hindering your weight loss efforts?
Media Fail: Busting the water "Myth"

References:

---

[i] Influence of water drinking on resting energy expenditure in overweight children. Dubnov-Raz, et al. Intl J Obes 2011;35(10):1295-1300.

[ii] Water-induced thermogenesis. Boschmann, et al. J Clin Endocrinol Metab 2003;88(12):6015-9.

[iii] Water Drinking Induces Thermogenesis through Osmosensitive Mechanisms. Boschmann, et al. J Clin Endocrinol Metab 2007;92(8):3334-3337.

[iv] Water-Induced Thermogenesis Reconsidered: The Effects of Osmolality and Water Temperature on Energy Expenditure after Drinking. Brown, et al. J Clin endocrinol Metab 2006;91:2598-3602.

[v] Cardiovascular and metabolic responses to tap water ingestion in young humans: does the water temperature matter? Girona, et al. Acta Physiologica 2014;211(2):358-370.

[vi] Water-induced thermogenesis and fat oxidation: a reassessment. Charriere, et al. Nutr Diabetes 2015;5:e190.

[vii] Negative, Null and Beneficial Effects of Drinking Water on Energy Intake, Energy Expenditure, Fat Oxidation and Weight Change in Randomized Trials: A Qualitative Review. Stookey, JD. Nutrients 2016;8(1):19.

The 2016 Dieting Season is Off and Running...

After 22 years in this field I have to admit that I periodically get burnt-out on taking the time to read and review new diet books or websites!

Nearly 20 years ago Kelly Brownell PhD once likened fad-diets to trick candles that keep re-lighting when you try to blow them out. Each new crop of books (or websites) invariably claim, “to contain the REAL secrets to weight loss.” This of course is just basic marketing and it’s very effective, especially when the average consumer “knows” more misinformation than fact regarding human metabolism, energy balance, and body weight.

Since it’s January, I thought I’d take a look at what’s “hot” on the diet landscape

Click to read more ...

Weight Training and Weight Control...

Strength training has lots of benefits -- for people of all ages -- and ideally it should be a component of a balanced overall fitness program. However, for the average person (following the average gym-based workout routine) it won't have a clinically significant affect on their Resting Metabolic Rate.

Click to read more ...

"Fat-Burning" Workouts: Founded in Fact or Fiction?

We see a lot of claims about the so-called "fat-burning" properties of various eating styles, foods, supplements and exercise modes. On that track I am reposting my blog from a few months ago on "fat-burning" workouts. The rest of these fat-burning claims will be the subject of future blogs, so stay tuned!

At some point you’ve probably heard the term “fat-burning,” and if you’ve ever set foot on a piece of cardio equipment it probably had a “fat-burning” mode. The implication is that there is something especially important about burning fat in maximizing weight loss.

Click to read more ...