Clinical Reviews

By Bill Campbell, Ph.D.
Exercise and Performance Nutrition Laboratory
University of South Florida

A great way to adhere to a low-carbohydrate diet is to consume a high-quality protein-rich meal replacement (with low carbohydrate content) such as Eat-Smart®.

Low Carb or Low Fat Diets for Weight Loss? Which One Really Works Best?

Shai I, Schwarzfuch D, Henkin Y, et al. Weight Loss with a Low-Carbohydrate, Mediterranean, or Low Fat Diet. N Engl J Med. 2008 Jul 17;359(3):229-41.

Opinions are still divided when it comes to which type of diet is more effective for weight loss—a traditional low-fat diet or one that reduces carbohydrate intake. Researchers from Israel investigated three types of diets: a low-carbohydrate diet, a Mediterranean diet, and a low-fat diet.

What makes this study impactful is that it included 272 people and was conducted over a two-year period. This type of design is far superior to most weight-loss studies that follow subjects for an abbreviated amount of time (typically a few weeks to, at most, several months).

At the end of the two-year study, the authors reported that those individuals following the low-fat diet lost seven pounds. Those following the Mediterranean diet lost ten pounds. And those adhering to the low-carbohydrate diet lost 12 pounds of bodyweight. Clearly, the low-carbohydrate diet outperformed the other diets in terms of weight loss.

What makes the results of this study even more amazing is that those individuals assigned to the low-carbohydrate diet did not restrict total calories, total protein, or total fat intake. Conversely, the other two dietary groups were restricted to 1,500 calories per day for women and 1,800 calories per day for men.

In essence, the low-carbohydrate group was allowed to eat as much food as they wanted (while limiting carbohydrate intake) and still lost more bodyweight! Obviously, low-carbohydrate diets have limitations for those individuals who are athletes or who engage in endurance activities, but in terms of weight loss/fat loss, the evidence is accumulating that such diets are very effective.

Caffeine Improves Resistance Exercise Performance

Supplementing with caffeine, as found in Energize®, one hour before your workouts has been shown to improve weight-training and sprinting performance!

Hudson GM, Green JM, Bishop PA, Richardson MT. Effects of caffeine and aspirin on light resistance training performance, perceived exertion, and pain perception. J Strength Cond Res. 2008 Nov;22(6):1950.

Caffeine has been growing in popularity when it comes to performance improvements. And for good reason. Virtually every month, another new study reports positive results.

And this study from Baylor University is no different. The researchers compared the independent effects of caffeine and aspirin on muscular endurance as assessed by light resistance exercise bouts performed to failure.

Fifteen college-aged men participated in this double-blind study. Each subject ingested aspirin (10 mg per kg of bodyweight), caffeine (6 mg per kg of bodyweight), or a placebo one hour before performing leg extensions and seated arm curls. The weight was set at the participant's 12-repetition maximum (a resistance where the subject could perform no more than 12 repetitions).

Each subject was required to perform four sets each of leg extensions and seated arm curls with three minutes of rest between each set and five minutes of rest between these two exercises.

And there was a significant increase in total repetitions with caffeine compared with placebo and aspirin in leg extensions. Additionally, caffeine ingestion produced an increase approaching significance in the arm curl exercise as compared to aspirin and placebo.

The authors concluded that caffeine enhanced resistance training performance in leg extension and arm curl exercises, whereas aspirin did not.

The practical application to this study is that if you ingest caffeine-containing energy drinks or other supplements that contain caffeine, you should ingest them about an hour before your exercise or training routine to maximize their effectiveness.

Caffeine Ingestion Improves Sprint Performance Too!

Caffeine is just as effective for performance enhancement in whatever form you prefer.

Carr A, Dawson B, Schneiker K, et al. Effect of caffeine supplementation on repeated sprint running performance. J Sports Med Phys Fitness. 2008 Dec; 48(4):472-8.

Research on the performance-enhancing (ergogenic) effects of caffeine has primarily examined aerobic performance and has consistently shown a positive benefit. As demonstrated above, caffeine has also been shown to improve resistance exercise performance as well.

Recently, scientists examined the effects of caffeine ingestion on sprint performance and reaction time (perfect for sports such as baseball, soccer, basketball, and virtually any other sport which requires these two essential athletic abilities).

Six mg of caffeine per kg of bodyweight was ingested 60 minutes prior to a repeated-sprint running and reaction time tests. The authors reported that total sprint times across sets 1, 3, and 5 (departure every 25 seconds) was significantly faster after caffeine ingestion as compared to placebo ingestion. Similarly, total sprint times across sets 2 and 4 (departure every 60 seconds) was significantly faster after caffeine ingestion as compared to placebo ingestion.

There were no significant improvements to reaction time as a result of caffeine ingestion. The investigators concluded that caffeine ingestion 60 minutes prior to exercise can enhance repeated sprint running performance and is not detrimental to reaction times.

The results of this study and others show that caffeine has ergogenic properties in multiple modes of exercise performance—endurance, resistance exercise, and high-intensity exercise such as sprinting.

Core Stability and its Relationship to Strength and Power

Nesser TW, Huxel KC, Tincher JL, Okada T. The relationship between core stability and performance in division I football players. J Strength Cond Res. 2008 Nov; 22(6):1750-4.

Training to improve core stability is currently a very popular training methodology. The theoretical rationale behind core stability training is that it allows an individual to fully transfer the forces generated from the ground through the lower extremities, the torso, and finally to the upper extremities, and in some instances an implement (i.e., hitting a baseball, striking a tennis ball, etc.).

According to new research, core strength does positively influence sprint speed, vertical jump, and total body strength.

A weak core is believed to cause alterations in the transfer of energy, resulting in reduced sport performance and increased risk of injury. In general, research in this area is lacking, but it does appear that more well-designed studies are beginning to emerge. One such study was recently published in the Journal of Strength and Conditioning Research.

The purpose of this study was to identify relationships between core stability and various performance variables in NCAA division I football players. It was reported that total core strength (comprised of trunk flexion, back extension, and left and right bridge) was significantly correlated with sprint speeds, vertical jump, and total body strength (comprised of bench press 1RM, leg press 1RM, and clean 1RM).

Even though these correlations were significant, the authors reported that the correlations were weak to moderate. Further, the authors stated that increases in core strength would not contribute significantly to strength and power. More research needs to be conducted on core stability training to determine its effectiveness on strength and exercise/sports performance.

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