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Friday, April 30, 2010

Is Fructose Unhealthy?

There has recently been some concern from various sources that fructose might be unhealthy. The focus on fructose has likely been prompted by the widely increased use of high-fructose corn syrup to sweeten various foods and drinks such as sodas, iced tea, yogurt, and snacks. Yet fructose can also be found in relatively high amounts in fruits, especially apples, pears, grapes (including raisins), and pineapples, and even in vegetables such as tomatoes, cabbage and squash. Table sugar (sucrose) is a 50/50 amalgam of fructose and glucose, while high-fructose corn syrup is 55% free fructose and 45% free glucose, industrially manufactured from corn starch,

There is some fairly solid evidence supporting the negative health effects of fructose on mice, but the evidence concerning humans is much less conclusive. In human studies, fructose intake has been positively correlated with obesity (1, 2), especially fatty deposits around the waist, which is thought to be the most dangerous to health and, of course, detrimental to the 6-pack look. Fructose also increases blood triglycerides, a recognized risk factor for heart disease (3). All cells in the body can metabolize glucose, but only the liver can metabolize fructose, and high fructose consumption appears to load the liver with fatty deposits (4, 5). Also, fructose tends to suppress insulin and leptin, both of which are hormones that decrease appetite, while increasing ghrelin, which raises appetite (6, 7), thus possibly contributing to excess weight gain. However, there is little evidence that the fructose in high-fructose corn syrup is more damaging than the fructose in table sugar (typically sucrose from sugar cane).

Bottom Line
While more studies must be done to solidify the evidence on the effects of fructose on human health, it appears wise to avoid excessive intake of fructose. This can be accomplished by:
  • Completely avoiding foods and drinks containing high-fructose corn syrup
  • Limiting consumption of table sugar and any product with a high sugar content
  • Limiting fruit juice consumption, especially juice from apples and grapes
1. Lustig RH (2006). "Childhood obesity: behavioral aberration or biochemical drive? Reinterpreting the First Law of Thermodynamics". Nature clinical practice. Endocrinology & metabolism 2 (8): 447–58. doi:10.1038/ncpendmet0220. PMID 16932334.

2. Isganaitis E, Lustig RH (2005). "Fast food, central nervous system insulin resistance, and obesity". Arterioscler. Thromb. Vasc. Biol. 25 (12): 2451–62. doi:10.1161/01.ATV.0000186208.06964.91. PMID 16166564.

3. Bantle JP, Raatz SK, Thomas W, Georgopoulos A (2000). "Effects of dietary fructose on plasma lipids in healthy subjects". Am. J. Clin. Nutr. 72 (5): 1128–34. PMID 11063439.

4. Forristal, Linda (Fall 2001). "The Murky World of High-Fructose Corn Syrup". Weston A. Price Foundation.

5. Ouyang X, Cirillo P, Sautin Y, et al. (June 2008). "Fructose consumption as a risk factor for non-alcoholic fatty liver disease". J. Hepatol. 48 (6): 993–9. doi:10.1016/j.jhep.2008.02.011. PMID 18395287.

6. Teff, KL; Elliott SS, Tschöp M, Kieffer TJ, Rader D, Heiman M, Townsend RR, Keim NL, D'Alessio D, Havel PJ (June 2004). "Dietary fructose reduces circulating insulin and leptin, attenuates postprandial suppression of ghrelin, and increases triglycerides in women". J Clin Endocrinol Metab. 89 (6): 2963–72. doi:10.1210/jc.2003-031855. PMID 15181085.

7. Swan, Norman; Lustig, Robert H. "ABC Radio National, The Health Report, The Obesity Epidemic". Retrieved 2007-07-15.

Thursday, April 29, 2010

Complex, Specific Training Improves Sports Performance

It is much more difficult to improve the physical performance of highly trained athletes than of previously untrained subjects. Thus, it is noteworthy that the study described below by Alves et al. (Journal of Strength and Conditioning Research, vol 24, no 4, pages 936-941, 2010) produced significant performance improvement among elite young Portugese soccer players using brief exercise sessions once or twice per week.

Experimental Method
23 young elite soccer players underwent the following tests before and after an 8-week period:
  • vertical jump from a static, bent-knee position
  • vertical jump using a dynamic countermovement (natural quick knee bend)
  • 5 meter sprint
  • 15 meter sprint
  • soccer agility test
All subject initially did 2 weeks of general weight training before being divided into 3 experimental groups that did the following for 6 weeks in addition to their normal soccer training:

Group 1 - Once a week, before their regular soccer training session, they went through the following 3 exercise stations:
  1. 6 reps of squats with 85% of max weight, 5 meters of high-knee skipping, 5 meter sprint
  2. 6 reps of calf raises with 90% of max weight, 8 vertical jumps, 3 soccer-ball high-head hits
  3. 6 reps of knee extension with 80% of max weight, 6 jumps from seated position, 3 60-cm drop jumps
Group 2 - The same routine as Group 1, but done twice a week instead of once a week.

Group 3 - Control group - did no exercises supplementary to their regular soccer practice.

5-meter sprint time improved 9% for Group 1 and 6% for Group 2
15-meter sprint time improved 7% for Group 1 and 3% for Group 2
vertical jump from static bent-knee position improved 13% for Group 1 and 10% for Group 2
none of the groups improved significantly in the countermovement jumps or agility test
the control group did not improve in any of the tests

A relatively short exercise program of weight-lifting, jumping, and sport-specific movements performed once or twice per week can significantly improve the physical performance of elite athletes. Even though the results of the once per week and twice per week exercise groups did not differ significantly, it appears that the subjects responded better to doing the program once per week rather than twice per week when regular sport training was persued concurrently.

Friday, April 23, 2010

Can Omega-3 Oils Deter Aging?

An interesting article appeared in the April 2010 Nutrition Action Health Letter that reported on a study of 600 San Francisco area residents with heart disease. Those with the highest blood levels of the Omega-3 fats, DHA and EPA, had the least telomere shortening, while those with the lowest blood levels had the most shortening. This is important because telomeres are the end-sections of chromosomes that become shorter as we age, eventually triggering genes that bring about symptoms of aging. These results were independent of other factors that might affect risk, like blood pressure, body weight, smoking history and exercise participation. The health letter recommends eating fatty fish like salmon twice a week and the American Heart Association recommends that people with heart disease take one 1,000 mg fish oil capsule daily. More than 3,000 mg per day may cause bleeding.

NOTE: This was a cross-sectional study. More definitive conclusions about the effects of Omega-3 fats on telomeres would be gained from prospective studies in which half the subjects are randomly assigned to eat high Omega-3 diets for several years while the other half are assigned to eat low Omega-3 diets, and the effects on their telomere shortening are observed. Of course, it is still a good idea to eat fatty fish because of the abundant existing evidence of it's disease-deterring qualities. Also, some of the countries with the longest life spans have high percapita fish consumption.

Tuesday, April 20, 2010

Static Stretching Reduces Jumping Power

In static stretching, a muscle is stretched to the point of mild discomfort and the position is held for 15 sec or more. In contrast, dynamic stretching involves rapidly moving in and out of the stretched position. The former recommendation in favor of static stretching was based on the finding that it was effective for lasting improvements in flexibility. Thus, for many years, pre-competition static stretching was widely recommended for a broad range of athletes. However, recent studies, such as the one described below, have shown that static stretching before athletic efforts requiring explosive power (e.g. sprinting and jumping) actually hurts performance.

Study Methods
In a study by La Torre et al. (Journal of Strength and Conditioning Research, vol 24, no 3, pages 687-694, 2010), 17 young men performed vertical squat jumps from a force-detecting platform using various starting knee angles. On one day, they did the jumps after performing static stretches of their quadriceps and calf muscles for 10 minutes. Each muscle was stretched on both legs using 4 sets of 30-second holds with 30-second rests between sets. On another day they did the jumps without stretching beforehand.

At all starting knee angles, stretching before the jump test reduced jump height, peak force, and maximal acceleration, but only the differences for jumps beginning with the knees least bent were statistically significant. When starting the jump with the knees flexed 50 degrees (about a half-squat position) jump height, peak force, and maximum acceleration were respectively 21%, 9%, and 15% lower when stretching was performed first than when no stretching was performed.

Bottom Line 
This study reinforces other ones showing that static stretching prior to an athletic event reduces explosive muscular power. The fact that the negative effect is most pronounced when the knees are only bent to a moderate degree is highly relevant to sports activities because most sports do not involve deeply bending the knee. Dynamic stretching does not have the same detrimental effect. Thus, it appears that before athletic events that require power but not great flexibility it is best to warm up thoroughly and perform dynamic stretches before the event. The detrimental effect of static stretching on muscular power has not been shown to carry over to the following day. Therefore, static stretching may be performed after an athletic event to promote general flexibility without harming physical performance.

Thursday, April 8, 2010

Brock Lesnar's Workout - Perfect Example of Functional Training

See the video of one of Brock Lesnar's workouts. Lesnar is the current top heavyweight of the Ultimate Fighting Championship (UFC), the most popular mixed martial arts organization in the U.S. He won the NCAA heavyweight wrestling championship in 2000 and later became a professional (choreographed) wrestler. When he joined the UFC, he became a dominant force. Watch this highlight video to see his speed and power.

Lesnar's workout is a prime example of functional training. No doubt weight-lifting and running are essential for a base level of fitness. However, to really excel in a sport or other physically demanding activity, one has to train in ways that simulate the activity to be improved. Lesnar's routine is based on 5-minute rounds as are UFC fights. His exercises are mostly whole-body, multi-directional, asymmetrical, and highly taxing to the lactic-acid energy system. No doubt Lesnar does a lot of conventional weight-liting. However, his lesson to us is that, in order to excel in a sport or other physical activity, training must be supplemented by routines that simulate the target activity as to which muscles and energy systems are used and the way they are used.

Tuesday, April 6, 2010

Vibration Training Can Increase Jump Height

Because of evidence supporting their effectiveness for improving strength, flexibility and power, whole body vibration platforms have become increasingly available in fitness centers and athletic training facilities. These platforms generally provide repeated vertical fluctuations at a user-selected rate and amplitude (distance). One study reported that frequencies of 20-30 Hz (cycles per second) produced the greatest gains in flexibility and strength. Amplitude adjustment generally ranges from 1-15 mm (0.04-0.60").

While it is easy to train previously untrained people to increase strength and power, it is more difficult to produce improvement in those already trained. Thus, the study described below provided a challenge to whole-body vibration training.

Experimental Method
In a study by Wyon, Guinan, and Hawkey published in the Journal of Strength and Conditioning Research (vol 24, no 3, pp. 866-870, 2010) 18 female undergraduate dance majors, who were currently engaged in 12-16 hours of dance training per week, were divided into the following two groups that were tested before and after a 6-week experimental period:

Experimental Group: In addition to their normal dance training, these subjects did whole-body vibration training two times a week separated by 2 rest days. The training consisted of twice holding each of the following positions for 30 sec while on a vibration platform set at a frequency of 35 Hz and amplitude of 4 mm (0.16").

     Half-squat with knees pointing outwards
     Right leg leading lunge
     Left leg leading lunge
     Maximal height calf raise
     Forward torso bend (at least 90 degrees) with knees straight

Control Group: In addition to their normal dance training, this group held each of the same positions as the experimental group, but on a stable floor rather than on a vibration platform.

The experimental groups improved 2.3 cm (0.9" or 6%) in their maximal vertical jump, while the control group actually declined by 1.5 cm (0.6" or 4%). This difference was statistically significant.

Bottom Line
Whole-body vibration training appears to hold promise for training athletes and dancers. The experimental training required only 5 minutes twice a week. Because the physical demands on in-season dancers and athletes are great, strength and power training is usually limited to avoid overtraining. However, whole-body vibration training seems to be able to improve performance without excessively stressing the athlete. An added advantage is the previous evidence that such training can improve bone mineral density. Low bone density has been a problem with female dancers and athletes who maintain low bodyfat, such as gymnasts and distance runners.