Are Low Carbohydrate Diets Best for Weight Loss?

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If you haven’t been bombarded with advertising for low carbohydrate foods, diets, plans and crazed anti-carbohydrate friends and coworkers in the past few years, you must be living on a remote island somewhere (taking any visitors?). The anti-carbohydrate, pro-fat crowd (including keto, Paleo, and Whole 30 – aka Paleo reinvented) devotees might be onto something. But that “something” isn’t a miraculous cure for obesity. Should you trade your low fat, higher carbohydrate diet for full fat foods and “bread” made from cauliflower and mozzarella cheese? It’s time to look past the media headlines to the latest research on low fat vs. low carbohydrate diets.

In this article I’ll cover:

  • the latest research on lower carbohydrate diets;
  • what this research means for you; and
  • a sidenote on the insulin hypothesis.

Should you switch to low carbohydrate vs. high carbohydrate foods?

The Latest Research on Low Carbohydrate Diets

In an attempt to determine which diet is best for weight loss, one of the latest studies collected and analyzed studies on low fat and low carbohydrate diets. A systematic review and meta-analysis, which combines the results of several studies, compared intervention studies > 1 year in length where participants were placed on low fat diets, low carbohydrate diets, other high fat dietary interventions or they continued eating whatever they wanted (their typical diet). Low fat diets ranged from  < 10% of calories from fat to < 30% of calories from fat. The diet interventions used ranged from providing instructions at the start of the study and expecting participants to follow the diet plan to regular counseling sessions with dietitians, food diaries and cooking lessons to actual feeding studies where participants were given most of their overall food intake (with the last approach the most well-controlled). Some studies coached participants to cut calories while others, including those put on low-carbohydrate Atkins-style diets, were told to eat until they were full without worrying about calories.

They analyzed results from 13 trials that examined weight maintenance as well as studies that didn’t include weight loss as a primary goal. In these studies low-fat and high-fat diets lead to a similar amount of weight loss. Low-fat diets were superior only when compared to the subjects’ normal diet – in other words actually going on a diet led to greater weight loss than not dieting (no surprise there). The tiebreaker came from an analysis of 35 weight loss trials, 29 of which were conducted using adults who were overweight, obese, or had type II diabetes. Overall, there was no difference between low-fat and high-fat diet interventions. Low-fat diets led to greater weight loss compared to groups who didn’t diet. However, higher fat diets were the clear winner (according to the headlines), leading to significantly greater weight loss after a year than low fat diets. Before tossing out your steel cut oatmeal, whole-grain bread and fresh Summer fruit, let’s take a closer look at this data. It was pulled from a comparison between low-fat diets and high-fat diets that varied by more than 5% of calories. So did low carbohydrate, higher fat diets really win or was it because subjects cut calories? Is it easier to cut calories on low carbohydrate, high fat diets? Participants on low carbohydrate diets lost about 2.2 pounds more weight after one year versus those on a low-fat diet. A 2.2-pound difference in weight loss after one year on a diet isn’t very impressive, especially considering many of the subjects were overweight or obese to begin with.

The End of Higher Carbohydrate, Low-Fat Diets?

Based on these results the authors suggest low-fat diets shouldn’t be the go-to recommendation for weight loss. However, the results of this study are mainly applicable to overweight, obese and type II diabetics – the primary populations examined in these studies. We can’t take the authors conclusion that low carbohydrate, higher fat diets are better if you are looking to lose a few pounds for a beach ready body. What works for an obese adult or type II diabetic will not necessarily work for an active adult who wants to get a 6-pack. Secondly, previous research shows low carbohydrate diets tend to produce greater weight loss, initially, than low fat diets (some of this is water weight since carbohydrates store 3-4 times their weight in water in the form of glycogen in muscles and the liver and your glycogen stores will start dropping when you drastically lower your carbohydrate intake) yet after a year, weight loss is equivalent between both diets. Other research shows weight loss over the first six months on a diet is the main predictor of both weight loss success and sticking to a diet over the long-term. Greater weight loss initially = better adherence = better success over time.

Long-term Success

What’s more disappointing than the paltry 2.2-pound difference between the low-fat and high-fat diets after one year is the total average weight loss in the studies designed for weight loss – a mere 8.25 lbs. after 1 year. Instead of declaring low carbohydrate, higher fat diets a clear winner over low fat, higher carbohydrate diets (especially considering the 2.2 pound difference), we should be asking why it’s tough to stay on a diet, any diet? Why aren’t study participants losing more weight? I don’t have the answer to these questions and leading weight loss researchers don’t seem to have a complete picture right now either.

If you want to lose weight, choose a lower calorie diet primarily based on high quality foods or create your own plan that fits into your lifestyle and is one you can stick with it. There are many diets that could, potentially, work for you. If you want to try a low carbohydrate diet for a while, by all means go for it (especially if you need to see that number on the scale move pretty quickly)! If cutting carbs sounds like being in detention, then skip that approach! I’m giving you permission to alter your plan as often as you need to based on changes in your lifestyle (some research papers actually suggest doing this and I am a huge fan of this approach), motivation, and results.

Conceptually, low carbohydrate diets are very easy. You don’t have to worry about portion sizes, log calories, count points or determine if you have to eat less at dinner to make up for a lunchtime splurge. Decision-making is boiled down to: it contains carbs and therefore off my diet or it is low in carbs and the carbs it does contain are high in fiber so I can eat it. Just don’t buy into the hype that low fat, higher carbohydrate diets are the only way to lose weight or that these diets are better, over the long term, than other dietary approaches that also cut calories.

References

Tobias DK, Chen M, Manson JE, Ludwig DS, Willett W, Hu FB. Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systematic review and meta-analysis. Lancet Epub before print. 29 October 2015.

Greenberg I, Stampfer MJ, Schwarzfuchs D, Shai I; DIRECT Group. Adherence and success in long-term weight loss diets: the dietary intervention randomized controlled trial (DIRECT). J Am Coll Nutr 2009;28(2):159-68.

Franz MJ, VanWormer JJ, Crain AL, Boucher JL, Histon T, Caplan W, Bowman JD, Pronk NP. Weight-loss outcomes: a systematic review and meta-analysis of weight-loss clinical trials with a minimum 1-year follow-up. J Am Diet Assoc 2007;107(10):1755-67.

Hall KD. Predicting metabolic adaptation, body weight change, and energy intake in humans. Am J Physiol Endocrinol Metab 2010;298(3):E449-66.

Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011; 378(9793).

Rosqvist F, Iggman D, Kullberg J, Cedernaes J, Johansson HE, Larsson A, Johansson L6, Ahlström H, Arner P, Dahlman I, Risérus U. Overfeeding polyunsaturated and saturated fat causes distinct effects on liver and visceral fat accumulation in humans. Diabetes 2014;63(7):2356-68.

 

 

 

Should Endurance Athletes Switch to a Low Carbohydrate Diet?

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High carbohydrate pasta with tomatoes
Pasta – a typical meal for endurance athletes.

Should endurance athletes trade in their high carbohydrate gels, gummies, and pasta for fatty steak and butter?  A recent study found elite ultra-marathoners and iron distance triathletes on a low carbohydrate diet  burned significantly more fat while running than  their counterparts on a typical higher carbohydrate diet. There was no difference in the level of glycogen depletion between groups after a 3-hour run.

Why Carbohydrates Matter

For several decades endurance athletes have relied on a carbohydrate rich diet to fuel their training and performance. Carbohydrates are the primary source of energy used during activity. They’re also a fast fuel – your body can use gels, gummies and sports drinks very quickly while also accessing the carbohydrates stored in your muscle when your energy needs outpace how quickly you can squirt more gel in your mouth. Regular intake of carbohydrates during  prolonged activity provides an important source of energy for working muscles and helps spare dipping into your reserves in muscle tissue (in the form of glycogen). Once glycogen levels start getting too low, your performance will subsequently decline.

If carbohydrates are important for performance why would anyone go on a low carbohydrate diet?

The longer you run, bike, swim or exercise in general, the more carbohydrates you need to keep up with energy demands. There are three main reasons athletes (particularly ultra endurance athletes) want an approach that doesn’t require carbohydrate during long bouts of exercise are:

  1. Your taste buds get tired –  Eat any food over and over again and you will get sick of it eventually. Now imagine running 30, 50 or 100 miles and eating a gel every 30 minutes. The consistency, sweetness and flavors will make your taste buds revolt.
  2. Your stomach might get upset. Exercise + eating (even seemingly easy to digest carbohydrate products) can cause stomach upset in some people.
  3. You are trying to lose body fat. If you are exercising for long periods of time it may sound counterintuitive to consume 30-60 grams of carbohydrate (or 90+ depending on the type of carbohydrate, your stomach’s tolerance and the type of exercise you’re doing) each hour while training.

If any of these apply to you, a diet that doesn’t force your body to rely on carbohydrates for energy may sound very appealing.

The Study & the Low Carb Diets for Endurance Athletes

The body has amazing ability to adapt to changes in the macronutrient composition of your diet.  In other words, if you eat more fat you’ll burn more fat. If you are adapted to a low carbohydrate diet, you will rely on your body fat for fuel and will not need to consume gels, gummies or any other carbohydrates while running, biking or swimming. However, there is an adaptation period.  It takes time for your body to switch over from relying on carbohydrate to fuel activity to using primarily fat. The study subjects included elite male ultra-endurance athletes who habitually consumed a high carbohydrate diet (> 55% of calories from carbohydrate) and a separate group of those habitually consuming  a low carbohydrate diet (< 20% of calories from carbohydrate and > 60% from fat though the average was 70% from fat) for at least 9 months. Both groups slept, reported to the lab fasted and then drank a 343 calorie shake (the shake contained 4.3 grams of carbohydrate for the low carbohydrate group and  42.7 g of carbohydrate for the high carbohydrate group). Ninety minutes later they ran on a treadmill.

Results

As expected, the low carbohydrate high-fat diet group used a lot more fat when jogging then the high carbohydrate group (88% of calories from fat vs. 56% in the high carbohydrate group). They also used more fat at a higher intensity than the high carbohydrate diet group. They were able to use fat at a good rate – fat is typically a slow source of energy but the rate of fat use in this fat-adapted group was pretty compatible to the typical rate (but not the maximum) at which an athlete can use carbohydrates. Glycogen levels at rest, glycogen breakdown during exercise and re-synthesis after exercise was the same in both groups. * There was no difference in the amount of calories burned between the two groups.

Is This Diet Right for You?

Ultra endurance athletes can adapt to and train on a higher fat diet.  They can also do this without glycogen depletion – glycogen depletion can come with other negative consequences including potential suppression of immune system functioning.  At this time, we do not know if regularly following a lower carbohydrate diet = better endurance performance.

What you need to consider:

  • According to this study you will not burn more calories during exercise when on a low carbohydrate, high fat diet. ** See note below.
  • Your body needs at least 1 month to adjust. The first week will probably suck (you’ll feel terrible and have low energy).
  • You might not improve performance (we don’t know).
  • Can you stay on a low carbohydrate, high fat diet? Do milkshakes made of  heavy cream, olive oil, walnut oil and whey protein sound yummy? Is this diet practical for your lifestyle? If you answer yes to those 2 questions,  then it might be worth a shot. Work with a nutrition expert to ensure you are getting all of the fiber, vitamins, and minerals you need for performance and health.

* Keep in mind the results from this study are specific to endurance athletes.

** If weight loss is your goal, it makes no difference if you burn more fat during exercise if you aren’t burning more total calories in that exercise session. The only caveat here is if a low carb diet means you consume few to no calories during exercise. In this scenario, a low-carb diet may help you consume fewer total daily calories.