Do you have a good understanding of why your diet didn't work, or why it may have worked initially but you couldn't sustain it?  Millions of people diet, and dieting is a Billion dollar if not Trillion dollar industry.  The culture of body image and weight loss means big bucks for people looking to capitalize by marketing diet products and programs.
You've probably tried a few different diets and achieved similar results, or perhaps you experienced divergent results but a common regression to your original starting point - perhaps you ended up gaining more than you lost.  This is a common problem.  It's been said that we don't have trouble losing weight - people do it everyday.  Rather, we have trouble keeping weight off.  Why?

The reason....

Please watch, listen, and share the video lecture.

"I'm so unmotivated", "I need a new routine", "I need something different", "I got bored of my old program"...

Do these sentiments sound familiar?  I hear this stuff all the time, and it's one of the many things that drive me batty. 

I've been training for over 20 years, and I've been training others for just over a decade, so believe me when I tell you I've heard it all.  I know how the average person perceives exercise; I know their good habits and I know their bad habits; I know why most people start and stop exercising; I know the success and failure rates; I know what separates them from me.  I know this from experience, and I know this from the abundance of exercise physiology, psychology, behavioural, and epidemiological research.

There's always some new article or book that convinces people of the obscure missing piece to their daily regimen that will magically be the one thing that sends them over the top of whatever obstacle(s) have been keeping them back.  But I, as well as the scads of coaches who actually work with people one on one (not just write books or articles), know that those who fail to accomplish their goals, whether fitness-based or otherwise - do so because they neglect the fundamentals, the basics - not the nuances.

Fundamentals account for 90-95% of success, whereas nuances are largely unnecessary components of the bigger picture.  A machine can be "finely tuned", but it can nonetheless perform its job as directed without fine tuning.  Fine tuning just means it does the job with less wasted energy.  The irony when it comes to a goal like weight-loss is that wasted energy IS the goal.  The less efficient you are, the more energy you expend, and the more weight you lose.  In contrast, getting fitter is a process of becoming more efficient at a given task - whether physically (e.g. stronger muscles move weight easier), or physiologically (e.g. more and larger mitochondria and RBC's allow you to use oxygen more efficiently).  This is why, in part at least, you find it difficult to maintain your weight-loss momentum from month to month.  You've picked all the low-hanging fruit (the easy weight), and now you have to work a bit harder and/or longer to get more weight off.

If you have a fitness goal, which also accomplishes health goals by proxy, you only need to worry about doing the basics, repeatedly, over a long enough timeline to see your goals through, and with the intent of doing so as best you can while acknowledging that you can always improve:

1. Do not overfeed yourself - or starve yourself
2. Do not restrict or avoid foods or food groups
3. Be active, regularly - but not obsessively
4. Get enough sleep
5. Avoid "all-or-nothing" attitude towards life
6. Pay attention to what you are doing, and learn from your mistakes
7. Strive for excellence; do the best you can; do better over time

Do NOT worry about silly, dichotomous thinking and biohacking BS such as:

1. Should I eat all my carbs at the start of the day or at the end of the day?
2. Should I sleep all at once or take micro-naps through the day?
3. Should I eat low carb or low fat?
4. Should I go Vegan or Carnivore?
5. I should count every calorie...or...Calories don't count if I do this diet!
6. Tracking food is obsessive compulsive, so I'm going to intermittent fast instead and create a binge eating disorder - yay!
7. I should only do only the BEST exercises, otherwise exercise isn't worth doing!
8. I'm 44, overweight, poor diet, high BP, and no training experience or formal guidance in exercise.... time to start training for that marathon and eating only meal replacement shakes!
9. I need to eat only low-glycemic carbs, less than 25g at every other meal, across 10 meals per day, between the hours of 12pm and 8pm, paired with only lean or vegan protein, every other day on my rest days where I only do fasted, low-intensity steady-state cardio first thing after I wake up.  Unless I'm on a carb load refeed - in which case I eat only 2 meals per day, immediately after my workout if 1 hour or less, otherwise before my workout if 1 hour or more, at 1500 calories each, containing 200g of mixed carbs each meal, with fats as low as possible to speed up gastric emptying and maximally stimulate insulin to "drive nutrients into my cells", along with at least 0.1g per kg/bodyweight of leucine to stimulate muscle protein synthesis from a protein source that is either only lactose free, gluten free, egg-free, free-range, grass-fed, organic, and ethically butchered....unless it's Saturday - in which case YOLO!!!!!!!!

We need to stop this nonsense.  These examples are all indicative of behaviour that attempts to circumvent long term commitment to the process, in favour of an easier way to the prize.  There isn't one.  This is true in life, as well as fitness.  For this reason, I find it typical that those who fall for these shortcuts and empty promises of success without effort tend to display a similar kind of half-assed approach to their jobs and home life.  Your "new routine" should be seeing your current routine through to the end.  Are you bored with progress?  If you are bored it's because you're just going through the motions, and in the beginning that was enough to keep you interested.  If you're bored it's because you never identified what your goals were, and thus you don't know why you started your routine in the first place.  That or you need a reminder - progress is the goal, not entertainment.

How you do fitness, is how you do life, work, and family - "If you don't have time to do it right, when will you have time to do it over?" - John Wooden

I think most of understand that the immune system is the gatekeeper of our health.  It protects us against the proliferation of pathogenic microorganisms like bacteria, viruses, and fungi but is also involved in tissue repair following injury.  Our immune systems, much like other expressions of our physiology, possess adaptive function.  For example, once infected by a pathogen, adaptive immunity engages, developing specificity (antibodies) against those foreign bodies (antigens) as well as "memory" to mount a more efficient defense should the same pathogen return.
In some circumstances, our immune system can become functionally depressed (immunodepression), which can leave us more prone to infection.  Such circumstances include heavy training schedules coupled with the rigorous demands of competition (e.g. stress of expectations, dieting to make weight, overuse of stimulants, and interrupted sleep schedule), and overall unbalanced diet.  Chances are that if these circumstances describe your training routine, then you could be a prime candidate for immunodepression.

So what does some of the research indicate?

Peters and Bateman (1983) and Niemen et al. (1990) both described a 2 to 6-fold frequency of self-reported upper respiratory tract infections (URTI) in athletes who competed in long-distance foot races.  Mechanistically, acute bouts of physical exercise produce physiological reactions similar to the presence of infection: an increase in circulating white blood cells (proportionate to exercise duration and intensity), and increases in leukocyte modulators (e.g. acute phase proteins).  Hormones with immunomudulatory effects are also released in response to exercise (e.g. adrenaline, cortisol, GH, and prolactin).  After prolonged exercise, immunoglobulin and B-lymphocyte suppression occurs, creating a possible "window of opportunity" for ambient pathogens (Pederson and Bruunsgard 1995).

There are several angles from which training, particularly endurance training, affects our immune system, such as:

• chronic stress
  • insufficient recovery time
• dehydration
  • impaired thermoregulation
  • cardiovascular strain
  • cell volume affects regulation of metabolism
• inadequate caloric / nutrient intake
• nutrient depletion (even with good diet)
• environment

CHRONIC STRESS
Leukocytes comprise the bulk of the immune system in form and function.  Repeated bouts of intense or prolonged exercise, and the stress it incurs, can suppress their circulating numbers and functional capacities.
Drops in circulating glutamine have also been suggested as a cause for immunodepression, though this has not been sufficiently validated.
Muscle damage induced inflammation may also be a factor.
An increase in gut permeability may permit entry of gut bacterial endotoxins into circulation, though this is most only of concern with prolonged exercise in hot conditions.
The increased rate and depth of breathing may increase exposure to airborne bacteria and viruses, particularly in crowded, poorly ventilated environments.

NUTRIENT DEFICIENCY
Studies suggest that exercise increases nutrient utilization, and thus their requirements (i.e. amount needed to maintain health).    Nutrients however can be further divided more specifically into macronutrients (required in large quantity, i.e. >3g) and micronutrients (required in minute quantity, i.e. <3g).  With a balanced diet, sufficient intake of both macronutrients and micronutrients is hard to screw up.  However, exclusion diets or very low-calorie diets can create deficiencies in either group. 
Whether or not a "normal" diet is sufficient to accommodate these increased requirements is likely highly individual and dependent on the duration and type of training involved.  There is not a lot of evidence pointing to potential inadequacy in athletic groups, except in those athletes who are dieting or who fail to consume a well-balanced diet. 
That being said, it is thought that marginal deficiencies of vitamins in sedentary individuals may elicit small effects, but that those effects are amplified in highly active athletes.  Exercise may induce deficiencies through decreased absorption in the G.I. tract, increased sweat and urination, increased nutrient turnover, and bio-chemical adaptations to training (i.e. the faster and further you drive, the more fuel you need).

FAT SOLUBLE VITAMINS (A, D, E, K)
As long as you are not actively avoiding the following foods or food groups, you will not find yourself at risk of a deficiency.  Furthermore, fat-soluble vitamins are retained in your own fatty tissues, making deficiency less likely compared to the water-soluble vitamins.  Vitamins A and E are required for normal immune function.

• A - Liver, fish, dairy, eggs
• D - Liver, fish, eggs, dairy
• E - Liver, eggs, whole grains, oils & butter
• K - Liver, eggs, leafy greens, dairy
  

WATER-SOLUBLE VITAMINS (B1, B2, B3, B6, B12, C, Folic Acid, Biotin, Pantothenic Acid)  Of the following vitamins, B12 and Folic acid are directly involved in the formation of leukocytes (white blood cells) that defend the body against infection, with Ascorbic Acid (Vit C) being required for their normal functioning.

• B1 - Whole grains, legumes, potatoes, nuts
• B2 - Dairy, meat, liver, eggs
• B3 - Meat, liver, poultry, fish (can be synthesized with tryptophan)
• B6 - Meat, liver, poultry, fish, potatoes, bananas
• B12 - Meat, fish, shellfish, poultry, liver, eggs, dairy
• C - Citrus fruits, leafy greens, broccoli, potatoes, berries
• Folic Acid - Meat, liver, leafy greens, grains, legumes, fruit
• Biotin - Meat, milk, eggs, grains, most vegetables
• Pantothenic Acid - Liver, meat, dairy, eggs, most vegetables

The RDA for the above nutrients is set to cover about 97% of all healthy individuals who consume a "normal" diet.  However, it is also a couple of deviations off the actual requirement to avoid deficiency.  In other words, you can come up short of the RDA for any of these vitamins, and not actually be in danger of a deficiency.  This buffer allows for some genetic variation between people, including differences in age, gender, and size.  I think it should also be mentioned that missing the RDA one day and hitting it the next is normal and healthy, and you should not fuss about maintaining those levels each and every day.

MICRO and MACROMINERALS
At least 20 minerals are known to be essential to humans, with 14 trace elements being essential to maintaining health. The seven macrominerals are potassium, sodium, chloride, calcium, magnesium, phosphorus and sulfur, with copper, zinc, and iron representing some of the more familiar trace elements.

Of the minerals essential to health, a deficiency in any the following are known to impair immune function, slow healing, or increase infections in humans:

• Copper (organs, seafood, eggs, nuts, bananas, legumes)
• Iron (organs, eggs, red meat, oysters, molasses, flour, green vegetables, legumes)
• Selenium (meat, seafood, dairy, whole grains, nuts)
• Zinc (oysters, shellfish, beef, poultry, dairy, whole grains, vegetables)

Again, unless you purposely avoid any of the food examples listed above, deficiency in any of their associated minerals is rare.  However, as said before, athletes engaged in strenuous activity do have increased demands.  Regular exercise, especially in hot environments, incurs increased losses of multiple minerals in sweat and urine. 
Iron and Zinc deficiencies are not uncommon, and Iron losses in sweat can be as high as 0.3 mg iron / L of sweat.  Sweat production can be 2L / hour in hot conditions.  An athlete training for 2 hours in such conditions could lose 1.2 mg of iron.  Note that the RDA for Iron is set at 8 mg (18 mg for females), however the absorption rate of Iron in the gut is only about 10%.  This would require an additional 12 mg of additional dietary Iron to recoup losses due to sweat, essentially doubling an athletes daily requirement (from 8 mg to 20 mg). All that said, recorded Iron losses in sweat vary greatly.
Another thing to consider is that well-trained athletes have well-trained muscles possessing adaptations such as increased myoglobin concentration and red cell mass.  Such adaptations may further increase the requirement for Iron.  It would not be a great stretch to suggest that athletes with or in pursuit of larger muscles (hypertrophy) would naturally retain more Iron, justifying supplementation. 
A word of caution: Contrary to other minerals for which excess intake is balanced by increased urinary excretion, Iron can build up to toxic levels easily in the body when intake exceeds requirements.  Unless you are chronically anemic or have difficulty utilizing Iron from your diet, supplementation may not be warranted, even for athletes.

LOW-CARB DIET
Studies have demonstrated that subjects performing prolonged exercise on a low-carb diet (<10% of dietary energy) for several days, have markedly higher stress hormone and cytokine responses compared to moderate and high-carb diets (Gleeson et al. 1998; Mitchell et al. 1998).  Consuming carbohydrate during exercise attenuates several markers of stress and immunodepression, such as rising cytokines, cortisol, and epinephrine (Nehlsen-Cannarella et al. 1997); neutrophil:lymphocyte ratio; and slows T-cell diminution (Henson et al. 1998).  It should be stated that glucose is an important fuel source for immune cells, which have high metabolic rates.

PROTEIN DEFICIENCY
An overemphasis on carbohydrate consumption, combined with inadequate caloric intake, can potentiate a protein deficiency in athletes, for whom an increased protein requirement has been well-established.  The T-cell system is highly dependent on sufficient amino acid availability.  Protein energy malnutrition (PEM) depresses the number of fully-matured T-lymphocytes, impairs phagocytic cell function, and decreases cytokine production.

A lot of noise has been made over the decades regarding glutamine, over-training, and immune health, and reductions in circulating glutamine do occur as a consequence of prolonged exercise.  However, despite maintaining plasma glutamine concentration, the evidence to show that oral supplementation of glutamine actually affects immune function perturbations is lacking (Rohde et al. 1998; Walsh et al. 2000). 
Sure enough, a review by Hiscock and Pederson in 2002 concluded that falls in plasma glutamine concentration are not related to immunodepression.  Regardless, an additional intake of 20-30g of protein per day can restore depressed plasma glutamine levels in overtrained athletes.   Hooray for protein!

As a quick aside, intakes of many micronutrients beyond specific thresholds reduce immune responses.  The best approach is to eat a well-balanced diet, eat enough calories to support training needs, avoid training longer than 2 hours or consider a carbohydrate/protein supplement during your session, take days off, get enough sleep, and monitor mood and fatigue levels throughout your training season.

Resources:
Jeukendrup, Asker E, and Michael Gleeson. Sport Nutrition: An Introduction to Energy Production and Performance. Champaign, IL: Human Kinetics, 2010. Print.